The export oriented FTSE 100 was down 1.6%, while the more domestically oriented FTSE 250 shed 1.4% by 0719 GMT.
Britain is facing "very, very difficult" economic times and the government had to launch immediate action to ignite economic growth, Prime Minister Liz Truss said in defence of her tax-cutting budget.
Meanwhile, yields on British government bonds rose on Thursday, after they fell sharply on Wednesday when the Bank of England revived its bond-buying programme to quell a gilts sell-off that threatened pension funds in the country.
Consumer staples stocks weighed on the benchmark FTSE 100 index, with British American Tobacco sliding 2.9% as it traded without entitlement to its dividend payout. Banking stocks dropped 2% in early trading.
Miners declined 2.0% as copper prices struggled due to concerns of potential shortages from lower inventories. [MET/L]
(Reporting by Johann M Cherian in Bengaluru; editing by Uttaresh.V)