LONDON'S blue chip index failed to hold above 7,500 mark on Monday, despite support from stronger oil prices and a drop in the pound after fresh polls showed Conservatives losing steam ahead of the General Election.

The FTSE 100 ended the day higher by 0.3 per cent or 25.63 points at 7,496.34, buoyed in part by the weaker pound which tends to boost multinational stocks on London's top flight index.

However, the more domestically-focused FTSE 250 closed at a record high of 19,912.55 points, up 0.5 per cent on the day.

Sterling was down 0.3 per cent against the US dollar at 1.300 and dropped nearly 0.5 per cent versus the euro to 1.157, after an opinion poll showed a sharp fall in the Tories' lead over Labour since the parties published their manifestos last week.

The Survation survey for ITV's Good Morning Britain showed the Conservatives on 43 per cent, down five points on the previous week and nine points ahead of Labour who are up five on 34 per cent.

Kathleen Brooks, a research director at City Index, said a weakening of the pound on the back of the poll was not surprising, given an assumed Tory victory has helped push the pound up 500 points versus the US dollar since the snap election was announced last month.

"A landslide from May soothed pound traders as it removed the prospect of a rushed Brexit deal to fit in with an election that otherwise would have been due in 2020.

"It also meant that Theresa May would have been handed a stronger mandate that could have silenced some of the harshest Brexiteers in the UK backbenchers that could have made negotiations with Europe a little easier for the Prime Minister.

"If these scenarios fail to develop, then the pound's march above 1.30 could be disrupted, at least in the short term."

Across Europe, the French Cac ended the day flat, while the German Dax fell 0.15 per cent.

In oil markets, Brent crude was up 0.1 per cent at one month highs of $53.85 per barrel, on hopes that this week's Opec meeting in Vienna will result in an extension of production cuts into 2018.

In UK stocks, HSS Hire fell 0.5p to 53.25p as the tool supplier announced it had appointed Steve Ashmore as chief executive after John Gill stepped down last month.

Marks and Spencer Group shares were at the top of the FTSE 100, up 10.6p to 395.5p, after Jefferies upgraded the stock price target from 370p to 420p amid signs that the retailer was gaining favour among shoppers.

BP shares rose 1.8p to 473.95p after the oil giant announced the start of production from its Quad 204 project offshore from the UK, marking a return to growth for its North Sea business.

The biggest risers on the FTSE 100 were Marks and Spencer Group up 10.6p to 395.5p, Burberry up 42p to 1,756p, Merlin Entertainment up 11.5p to 525.5p, and Paddy Power Betfair up 180p to 8,560p.

The biggest fallers on the FTSE 100 were Hikma Pharmaceuticals down 80p to 1,656p, Micro Focus International down 93p to 2,379p, Worldpay Group down 7.8p to 314.1p, and Direct Line Insurance Group down 4.4p to 347.3p.