The FTSE 100 rose to an intra-day record high on Monday, as energy stocks were given a boost by a jump in oil prices.
The UK's blue-chip index reached 7,460 points in early morning trading before falling back to 7,450 points, after climbing to a record high on Friday.
Oil and gas companies, which make up 13.6% of the index, benefitted from the rise in oil prices with Premier Oil up 3.8% to 61.25p while BP climbed 1.1% to 465p.
The rise in oil prices came after Saudi Arabian and Russian ministers agreed supply cuts should extend into 2018. This is far beyond the optional six-month extension to the reductions of 1.8 million barrels a day included in the deal signed between OPEC and non-OPEC members last November.
Khalid al-Falih, Saudi Arabia's energy minister, said in an interview in Beijing: "We have come to the conclusion the agreement needs to be extended. It will probably be better to end cuts at the end of Q1 of 2018," according to Bloomberg.
Alexander Novak, Russian energy minister, said "preliminary consultations show that everybody is committed" to the output agreement and no country is willing to quit.
On the news, Brent crude rose 2.3% to $52.04 a barrel while West Texas Intermediate (WTI) climbed 2.6% to $49.09.
US shale producers have kept oil prices below Saudi Arabia's target of $60 a barrel, with supplies coming back online at faster rates than expected.
OPEC and non-OPEC countries will meet in Vienna on 25 May to decide whether they will extend the original cuts, which are due to end in June.
Shawn Reynolds, manager of the Natural Resources Equity strategy at VanEck, said: "We see this as an unprecedented degree of cooperation between the two largest producers in the world providing a degree of commitment and visibility unmatched in the OPEC-era.
"In our view, it also suggests that they believe the global crude market ultimately easily accommodates US shale oil production and that further US production growth may be needed as major conventional sources of supply suffer from the extraordinary reductions in capital spending in 2014-2017."
Unclear on job moves
Reforms not enough
McGhee joins from banking trade body
Our video series continues
In June 2016, immediately before the Brexit referendum, a curious thing happened.