Sales were up 3.6 per cent in April while they had jumped by 5.1 per cent in the same month last year.
The volcanic ash cloud which billowed across Europe grounded flights for six days so tourists were not able to reach the capital. Meanwhile many of those stranded in London had already spent their holiday money.
In another blow, Easter fell in March which meant that April was robbed of the traditional festive spending boost. Clothing and footwear sales slowed and homeware fell back despite heavy discounts and promotions.
Food sales were was also badly hit, mainly because they did not include the traditional Easter holiday purchases.
Helen Dickinson, Head of retail at KPMG, said: “Disruption to air travel caused by the Icelandic volcano affected the number of visitors to London, which is a key driver of performance.
“The timing of Easter, falling into March this year but in April last year, has also deflated the figures.”
Footfall – the measure of the number of shoppers on the streets – was 3.5 per cent down on the previous year. However, London sales growth was stronger than that of the UK as a whole, where like-for-like sales fell 2.3 per cent year-on-year, against a 4.6 per cent gain in April 2009.
Meanwhile the BRC figures showed that disruption to air travel caused by the Icelandic volcano affected the number of visitors to London, which is a key driver of outperformance.
BRC director general Stephen Roberston said: “The picture in London is nowhere near as bad as it looks. It looks like a dramatic slowdown in growth compared with March but it was mainly down to ash and the early Easter.”