Sterling has fallen sharply after Downing Street confirmed that it would trigger Article 50 next week.
The pound, which had risen against the dollar to a three-week high of $1.243, dropped to $1.237. It also fell against the euro, to €1.151.
The announcement that Britain’s formal departure from the European Union will begin next Wednesday unsettled traders. Shortly before noon the FTSE 100 was trading down 10 points, or 0.14 per cent, at 7,415, having set an all-time closing record on Friday of 7,424.96.
Royal Bank of Scotland was struggling. The state-controlled lender lost 3½p to 240½p; analysts suggested that some investors were taking short-term profits after good performances over recent days. Standard Chartered dropped 5¼p to 725p and Barclays fell 1½p to just shy of 229p.
As oil prices slipped BP fell 4½p to 485½p. Royal Dutch Shell also endured a difficult start to the week, trading down 10p at £21.13.
James Butterfill, executive director at ETF Securities, said that although strong US production had put prices under pressure over recent weeks things could be looking up. “Saudi Arabia may extend the Opec deal beyond the initial six months if inventory remains above the five-year average,” he said.
An upgrade from Goldman Sachs from “neutral” to “buy” sent Associated British Foods, which owns Primark, to the top of the market. Its shares gained 14p to £26.61.
The FTSE 250 also had a downbeat start to the week. Allied Minds led the fallers, shedding 16½p to 371p. IP Group was also under pressure, trading down 7p at 161½p, while Hill & Smith Holdings dropped 55p to £12.97. Overall, the index fell 24.56 points, or 0.13 per cent, to 19,070.35.