Goldman Sachs has retained its 'sell' recommendation for British department store group Marks & Spencer (M&S), saying that the business is not exempt from increasing competition in the UK grocery market.In a research report dated April 3rd, the bank added the stock to its 'Conviction Sell List' and slashed its target price for the shares from 420p to 340p."With circa 50% of its revenue [for the year ended March 2014] coming from UK grocery sales, we do not believe M&S will be immune to escalating competition in UK food retail," Goldman said.It said that its Food division is the key driver of footfall in store, with 45% of UK households shopping at M&S Food each year, according to company estimates. As such, the company is likely to invest in gross margin to "protect traffic", the bank said."In General Merchandise (GM), freehold and long leasehold stores leave little flexibility, acting as a barrier to exit as apparel sales move online and to prime retail locations. Hence, we expect long-term store margin pressure in GM to offset operational improvements."The comments came ahead of M&S' fourth-quarter trading update on April 10th, which Goldman expects will show flat like-for-like (LFL) sales in Food and another quarter of LFL declines in GM. "However, we believe the grocery market will become more competitive and we cut our 2016 profit before tax estimate by circa 20% as we incorporate a weaker than previously expected performance in both the UK Food and GM divisions."The stock was down 0.25% at 470.4p by 11:23 on Friday.BC