* FTSE 100, FTSE 250 up 0.1%
* Oil majors biggest boost to main bourse
* Midcap retailer Ted Baker surges on M&A reports (Adds company news, updates shares)
By Muvija M
July 22 (Reuters) - Gains in oil heavyweights amid heightened tensions in the Middle East helped London's main index hold steady on Monday, while Ted Baker was in demand after several media reports of takeover plans.
The FTSE 100 index of bluechip companies and the FTSE 250 midcap index both edged higher by 0.1%.
Oil majors Shell and BP rose about 1% each, tracking gains in crude prices on concerns that Iran's seizure of a British tanker last week may lead to supply disruptions in the Middle East.
Monday's gains in the midcap bourse were led by Ted Baker Plc with a 13.5% jump, after a media report that its founder Ray Kelvin could back a private equity buyout of the retailer, months after he resigned.
Tour operator TUI's London-listed shares rose 4.6%, topping the FTSE 100 leader-board after Stifel resumed coverage on the stock with a "buy" rating.
Just Eat added 2.3% after the online takeaway service said it would lay off "a number" of jobs in Britain as it combined its customer and restaurant operations.
Helped in part by expectations of interest rate cuts by central banks, the exporter-heavy FTSE 100 has recovered from a slump it had weathered in May due to global trade uncertainty, and is currently on course for its best year since 2016.
The index, whose components roughly two-thirds of profits in the U.S. dollar, has also benefited as Brexit jitters have pressured the pound.
According to polls and bookmakers, Boris Johnson will become Britain's new prime minister on Wednesday and will immediately face the riddle that is Britain's Brexit negotiation.
"Watch for a harder tone on Brexit and the very clear message that October 31st is a hard date. As previously argued, the reality of parliamentary arithmetic may see this soften in due course," Markets.com analyst Neil Wilson said.
Metro Bank advanced 6% after the troubled mid-cap lender confirmed a report that it was in talks on the sale of a loan portfolio.
The stock has plummeted 70% so far this year as an accounting error, which eventually led to a cash call and a warning on results, has spooked investors.
Weighing on the main index was Whitbread, which lost 4.4% after the company said it was not planning any further capital return to shareholders.
Among smaller stocks, Petra Diamonds tumbled 9% after it reported full-year revenue below analysts' estimates and said it expects next year's production to be slightly lower amid weak demand in the diamond market. (Reporting by Muvija M, additional reporting by Shashwat Awasthi and Samantha Machado in Bengaluru Editing by Shounak Dasgupta and Frances Kerry)