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* FTSE 100, FTSE 250 off 0.3% each

* Future up after Jefferies upgrades to "buy"

* Aston Martin falls on plans for new sportscar

June 26 (Reuters) - London stocks closed lower on Wednesday for the third straight session, mirroring European bourses, while energy shares weighed the most and investors were on edge ahead of the Federal Reserve's key inflation gauge set for release on Friday.

The blue-chip FTSE 100 edged 0.3% lower while the mid-cap FTSE 250 also slipped 0.3%.

The pound dipped 0.5% against the dollar, as investors funnelled funds into the greenback amid growing caution ahead of Friday's release of the personal consumption expenditures price index.

In the UK, investors will watch out for UK gross domestic product (GDP) on Friday for further clues on the direction of interest rates in Britain.

Moreover, Britain's parliamentary elections, scheduled for July 4, are adding to the caution, with investors expecting political uncertainty to impact markets.

The Oil and gas sector ticked 0.6% lower, tracking lower oil prices after U.S. EIA's report.

Precious and industrial metal miners were among the biggest gainers among FTSE 350 sub sectors.

Future Plc gained 8.3% after Jefferies upgraded the stock to "buy" from "underperform" and hiked it's price target.

Aston Martin lost 2.6% after it announced the debut of a new limited edition sportscar car, Valiant. (Reporting by Purvi Agarwal in Bengaluru; Editing by Savio D'Souza, Alexandra Hudson)