diff --git a/app/services/bulk_upload/sales/year2023/csv_parser.rb b/app/services/bulk_upload/sales/year2023/csv_parser.rb
new file mode 100644
index 000000000..ca24bf937
--- /dev/null
+++ b/app/services/bulk_upload/sales/year2023/csv_parser.rb
@@ -0,0 +1,91 @@
+require "csv"
+
+class BulkUpload::Sales::Year2023::CsvParser
+  MIN_COLUMNS = 135
+  MAX_COLUMNS = 142
+
+  attr_reader :path
+
+  def initialize(path:)
+    @path = path
+  end
+
+  def row_offset
+    if with_headers?
+      rows.find_index { |row| row[0].match(/field number/i) } + 1
+    else
+      0
+    end
+  end
+
+  def col_offset
+    with_headers? ? 1 : 0
+  end
+
+  def cols
+    @cols ||= ("A".."EK").to_a
+  end
+
+  def row_parsers
+    @row_parsers ||= body_rows.map do |row|
+      stripped_row = row[col_offset..]
+      hash = Hash[field_numbers.zip(stripped_row)]
+
+      BulkUpload::Sales::Year2023::RowParser.new(hash)
+    end
+  end
+
+  def body_rows
+    rows[row_offset..]
+  end
+
+  def rows
+    @rows ||= CSV.parse(normalised_string, row_sep:)
+  end
+
+  def column_for_field(field)
+    cols[field_numbers.find_index(field) + col_offset]
+  end
+
+private
+
+  def default_field_numbers
+    [6, 3, 4, 5, nil, 28, 30, 38, 47, 51, 55, 59, 31, 39, 48, 52, 56, 60, 37, 46, 50, 54, 58, 35, 43, 49, 53, 57, 61, 32, 33, 78, 80, 79, 81, 83, 84, nil, 62, 66, 64, 65, 63, 67, 69, 70, 68, 76, 77, 16, 17, 18, 26, 24, 25, 27, 8, 91, 95, 96, 97, 92, 93, 94, 98, 100, 101, 103, 104, 106, 110, 111, 112, 113, 114, 9, 116, 117, 118, 120, 124, 125, 126, 10, 11, nil, 127, 129, 133, 134, 135, 1, 2, nil, 73, nil, 75, 107, 108, 121, 122, 130, 131, 82, 109, 123, 132, 115, 15, 86, 87, 29, 7, 12, 13, 14, 36, 44, 45, 88, 89, 102, 105, 119, 128, 19, 20, 21, 22, 23, 34, 40, 41, 42, 71, 72, 74, 85, 90, 99].map do |h|
+      if h.present? && h.to_s.match?(/^[0-9]+$/)
+        "field_#{h}"
+      else
+        "field_blank"
+      end
+    end
+  end
+
+  def field_numbers
+    @field_numbers ||= if with_headers?
+                         rows[row_offset - 1][col_offset..].map { |h| h.present? && h.match?(/^[0-9]+$/) ? "field_#{h}" : "field_blank" }
+                       else
+                         default_field_numbers
+                       end
+  end
+
+  def headers
+    @headers ||= ("field_1".."field_135").to_a
+  end
+
+  def with_headers?
+    rows.map { |r| r[0] }.any? { |cell| cell&.match?(/field number/i) }
+  end
+
+  def row_sep
+    "\n"
+  end
+
+  def normalised_string
+    return @normalised_string if @normalised_string
+
+    @normalised_string = File.read(path, encoding: "bom|utf-8")
+    @normalised_string.gsub!("\r\n", "\n")
+    @normalised_string.scrub!("")
+
+    @normalised_string
+  end
+end
diff --git a/spec/services/bulk_upload/sales/year2023/csv_parser_spec.rb b/spec/services/bulk_upload/sales/year2023/csv_parser_spec.rb
new file mode 100644
index 000000000..54af60e3d
--- /dev/null
+++ b/spec/services/bulk_upload/sales/year2023/csv_parser_spec.rb
@@ -0,0 +1,148 @@
+require "rails_helper"
+
+RSpec.describe BulkUpload::Sales::Year2023::CsvParser do
+  subject(:service) { described_class.new(path:) }
+
+  let(:file) { Tempfile.new }
+  let(:path) { file.path }
+  let(:log) { build(:sales_log, :completed, :with_uprn) }
+
+  context "when parsing csv with headers" do
+    before do
+      file.write("Question\n")
+      file.write("Additional info\n")
+      file.write("Values\n")
+      file.write("Can be empty?\n")
+      file.write("Type of letting the question applies to\n")
+      file.write("Duplicate check field?\n")
+      file.write(BulkUpload::SalesLogToCsv.new(log:).default_2023_field_numbers_row)
+      file.write(BulkUpload::SalesLogToCsv.new(log:).to_2023_csv_row)
+      file.rewind
+    end
+
+    it "returns correct offsets" do
+      expect(service.row_offset).to eq(7)
+      expect(service.col_offset).to eq(1)
+    end
+
+    it "parses csv correctly" do
+      expect(service.row_parsers[0].field_19).to eql(log.uprn)
+    end
+  end
+
+  context "when parsing csv with headers in arbitrary order" do
+    let(:seed) { rand }
+
+    before do
+      file.write("Question\n")
+      file.write("Additional info\n")
+      file.write("Values\n")
+      file.write("Can be empty?\n")
+      file.write("Type of letting the question applies to\n")
+      file.write("Duplicate check field?\n")
+      file.write(BulkUpload::SalesLogToCsv.new(log:).default_2023_field_numbers_row(seed:))
+      file.write(BulkUpload::SalesLogToCsv.new(log:).to_2023_csv_row(seed:))
+      file.rewind
+    end
+
+    it "returns correct offsets" do
+      expect(service.row_offset).to eq(7)
+      expect(service.col_offset).to eq(1)
+    end
+
+    it "parses csv correctly" do
+      expect(service.row_parsers[0].field_19).to eql(log.uprn)
+    end
+  end
+
+  context "when parsing csv without headers" do
+    let(:file) { Tempfile.new }
+    let(:path) { file.path }
+    let(:log) { build(:sales_log, :completed, :with_uprn) }
+
+    before do
+      file.write(BulkUpload::SalesLogToCsv.new(log:, col_offset: 0).to_2023_csv_row)
+      file.rewind
+    end
+
+    it "returns correct offsets" do
+      expect(service.row_offset).to eq(0)
+      expect(service.col_offset).to eq(0)
+    end
+
+    it "parses csv correctly" do
+      expect(service.row_parsers[0].field_19).to eql(log.uprn)
+    end
+  end
+
+  context "when parsing with BOM aka byte order mark" do
+    let(:file) { Tempfile.new }
+    let(:path) { file.path }
+    let(:log) { build(:sales_log, :completed, :with_uprn) }
+    let(:bom) { "\uFEFF" }
+
+    before do
+      file.write(bom)
+      file.write(BulkUpload::SalesLogToCsv.new(log:, col_offset: 0).to_2023_csv_row)
+      file.close
+    end
+
+    it "parses csv correctly" do
+      expect(service.row_parsers[0].field_19).to eql(log.uprn)
+    end
+  end
+
+  context "when an invalid byte sequence" do
+    let(:file) { Tempfile.new }
+    let(:path) { file.path }
+    let(:log) { build(:sales_log, :completed, :with_uprn) }
+    let(:invalid_sequence) { "\x81" }
+
+    before do
+      file.write(invalid_sequence)
+      file.write(BulkUpload::SalesLogToCsv.new(log:, col_offset: 0).to_2023_csv_row)
+      file.close
+    end
+
+    it "parses csv correctly" do
+      expect(service.row_parsers[0].field_19).to eql(log.uprn)
+    end
+  end
+
+  describe "#column_for_field", aggregate_failures: true do
+    context "when headers present" do
+      before do
+        file.write("Question\n")
+        file.write("Additional info\n")
+        file.write("Values\n")
+        file.write("Can be empty?\n")
+        file.write("Type of letting the question applies to\n")
+        file.write("Duplicate check field?\n")
+        file.write(BulkUpload::SalesLogToCsv.new(log:).default_2023_field_numbers_row)
+        file.write(BulkUpload::SalesLogToCsv.new(log:).to_2023_csv_row)
+        file.rewind
+      end
+
+      it "returns correct column" do
+        expect(service.column_for_field("field_1")).to eql("CO")
+        expect(service.column_for_field("field_99")).to eql("EK")
+      end
+    end
+
+    context "when no headers" do
+      let(:file) { Tempfile.new }
+      let(:path) { file.path }
+      let(:log) { build(:sales_log, :completed, :with_uprn) }
+
+      before do
+        file.write(BulkUpload::SalesLogToCsv.new(log:, col_offset: 0).to_2023_csv_row)
+        file.rewind
+      end
+
+      it "returns correct column" do
+        expect(service.column_for_field("field_1")).to eql("CN")
+        expect(service.column_for_field("field_99")).to eql("EJ")
+      end
+    end
+  end
+end