ONS Retail Sales Volume NSA
The Retail Sales Index (RSI) (volume, non-seasonally adjusted) measures the volume of retail sales in Great Britain on a monthly basis and does not adjust for seasonal variations (e.g. the timing of Easter). The volume estimates are calculated by taking the value estimates and adjusting to remove the impact of price changes, expressed as annual percentage growth compared with the same month in the previous year.
Office for National Statistics
Retail Sales Index
Subscribers can download 10 years' worth of data.