News of a potential new stumbling block on the UK’s road to negotiating a deal with the European Union before the end of the year sent the FTSE 100 soaring in London on Monday.
The FTSE jumped by nearly 2.4% as it benefited from a weak pound.
The Financial Times reported on Sunday that ministers were preparing a new bill which would overrule parts of the withdrawal agreement that was signed by the UK and the EU.
It sent sterling tumbling by 0.9% against the dollar to 1.3159, and by 0.7% against the euro to 1.1136.
The FTSE is populated by many exporters whose products become cheaper for foreign buyers when the pound falls.
It had risen by 138.32 points to 5937.4 at the close of play on Monday.
“The fall in the pound is helping the FTSE 100 outperform versus its eurozone equivalents,” said CMC Markets analyst David Madden.
“Firms that have a large international presence, such as AstraZeneca, Reckitt Benckiser, Diageo, Ashtead, Unilever, and GlaxoSmithKline, are all befitting from the drop in the pound.”
He added: “Sterling is under pressure over fears the UK and the EU might not strike a deal, and that would result in business being conducted on WTO terms in January.
“Yesterday, Prime Minister (Boris) Johnson said that if a free trade deal has not been agreed upon by October 15, it would be time to walk away from the trade talks and peruse a basic WTO style trading relationship with the EU, which would commence in 2021.”
Other European markets also had a strong day with the Dax in Germany up 2%, and the Cac 40 rising 1.8%.
US markets were closed for Labour Day, so remained unchanged.
In company news, shares in media company Future bounded more than 18% after it revealed that a surge in online readers will boost its profit.
The owner of FourFourTwo and TechRadar now expects full-year profit to be ahead of market after it saw a 25% jump in unique visitors in the UK.
Primark-owner AB Foods rose 0.5% after saying it would top profit forecasts as sales surged over the summer.
Sales at the clothes shop were “reassuring and encouraging” since they reopened in June, the company said.
The biggest risers on the FTSE 100 were Melrose Industries, up 6.75p to 122.3p, Scottish Mortgage Investment Trust, up 46.5p to 895.5p, Ashtead Group, up 132p to 2,693p, M&G, up 8p to 165.4p, and Experian, up 129p to 2,799p.
There were only three companies whose shares fell on the FTSE 100.
They were: IAG, down 10.2p to 209.2p, NatWest, down 1.15p to 106.65p, and British Land, down 1p to 351.8p.