Source: Sharecast
The FTSE 100 was called to open around 25 points lower. At 0720 BST, sterling was down 0.1% against the dollar at 1.3199.
Burnham comfortably won the by-election, defeating Reform UK's Robert Kenyon and securing a seat in parliament.
"Everyone knows that politics isn't working," he said in his acceptance speech. "Tonight could, just could, be the turning point."
"Burnham, on Labour's left wing, has pledged to respect existing fiscal rules, but worries in gilt markets are kept very much alive," said Danske Bank.
Investors will also be mulling the latest retail sales and borrowing figures.
Data released earlier by the Office for National Statistics showed that retail sales rose more than expected in May, helped along by good weather and promotions. Retail sales ticked up 1.2% following a 1% decline in April, coming in comfortably ahead of analysts’ expectations for a 0.5% increase.
Separate figures from the ONS showed that government borrowing rose more than expected in May.
Borrowing - the difference between total public sector spending and income - came in at £23.3bn, up £5.4bn on May 2025 and £5.6bn more than the £17.7bn forecast by the Office for Budget Responsibility.
In corporate news, Barratt Redrow said it had appointed former Britvic and British Airways executive Rebecca Napier as chief financial officer with effect from 3 August.
Most recently CFO of Britvic until its acquisition by Carlsberg Group in 2025, she previously spent 17 years at IAG, including as CFO of British Airways. Napier began her career at Deloitte, having qualified as a chartered accountant, the housebuilder said.
PPHE Hotel Group said that its independent committee had concluded that the £22 per share indicative offer from Fattal Hotel Group would not proceed after major shareholder Euro Plaza Holdings signalled its opposition.
Fattal submitted an indicative cash proposal in May, which the board judged to represent fair value. However, an independent committee was formed and consulted shareholders representing around 83% of the register, with Euro Plaza, which owns a roughly 33% stake in PPHE, telling the committee it opposed the deal.
PPHE added that it received a separate early‑stage approach from another party on 31 May, which was now being assessed.