The FTSE 100 was down 0.6%, while the FTSE 250 shed 0.4% by 0718 GMT.
The British government reversed plans to cut the highest rate of income tax that sparked a turmoil in financial markets last week and saw the mid-cap index mark its worst weekly decline since March.
The sterling was up 0.4% as opposed to a near 4% decline following the tax cut announcement on Sept. 23. [GBP/]
Banking stocks were off by 0.6%, while consumer companies such as British American Tobacco and Unilever tumbled 0.8% each.
Ratings agency Standard & Poor had cut the outlook on Friday evening for its AA credit rating for British sovereign debt to "negative" from "stable" as it judged Prime Minister Liz Truss's tax cut plans would cause debt to keep rising.
UK manufacturing data for the month of September is not expected to have changed compared with August, data due at 0830 GMT is expected to show.
(Reporting by Johann M Cherian in Bengaluru; Editing by Savio D'Souza)