LONDON, July 8 (Reuters) - British retailer Marks & Spencer's underlying non-food sales fell for a 12th straight quarter, it said on Tuesday, hurt by the transition to a new web platform.
The firm said sales of non-food products, spanning clothing, footwear and homewares, at stores open over a year fell 1.5 percent in the 13 weeks to June 28, its fiscal first quarter.
That compares with analysts' forecast in a range of down 1-2 percent and a decline of 0.6 percent in the fourth quarter of M&S's 2013-14 year.
M&S cautioned in May that its new website, which went live in February, would take up to six months to "settle in". It said this was normal for the industry and denied there were problems with the site.
The firm said M&S.com sales fell 8.1 percent in the first quarter.
Within the non-food like-for-like figure M&S said clothing like-for-like sales fell 0.6 percent, having risen 0.6 percent in the fourth quarter.
M&S's food business, which contributes over half of group sales but less profit, is performing much better, delivering a 19th consecutive quarter of growth.
Its sales on the same basis rose 1.7 percent, versus analysts' forecasts of up 1.5-2.5 percent and a fourth quarter rise of 0.1 percent.