The FTSE 100 was down 0.1 percent, snapping a six-day winning streak, while the FTSE 250 was roughly flat by 0826 GMT.

BP, which led the index higher with a more than 5 percent gain on Tuesday after strong results, dipped along with other oil stocks as crude prices fell.

Trump's renewal of a demand for $5.7 billion in funding to build a U.S.-Mexico border wall also stoked fears of another U.S. government shutdown, helping keep Asian stock markets subdued overnight.

Investors sold off UK financial stocks after France's largest listed bank, BNP Paribas, cut its 2020 targets, while GlaxoSmithKline was 1.4 percent lower ahead of its full-year results later on Wednesday.

CYBG, a newly emerged challenger to Britain's big retail banks, jumped 12 percent on track for its best day on record after reporting a rise in first quarter lending.  Peer Metro Bank, which was battered after reporting an accounting error last month, also rose.

Online retailer Ocado shed 7 percent after saying  operations at its flagship automated distribution centre in Andover were suspended after a fire broke out in part of the site.

Irish building materials group CRH gained 4 percent and outperformed the main index after a Reuters report that activist investor Cevian Capital had built a stake in the group.

Britain's biggest housebuilder Barratt rose 2.6 percent after it posted higher first-half volumes and, in relation to Brexit, said it was working with suppliers to ensure continuity of supply of overseas components.

The Telegraph reported late on Tuesday that UK cabinet ministers had secretly held talks on plans to delay Brexit by eight weeks, potentially postponing Britain's exit from the bloc to May 24.

Small-cap support services provider Interserve opened lower but quickly erased losses to surge 13 percent after striking a deal with creditors to more than halve its debt by issuing new shares.