(Reuters) - Britain's main stock indexes rose on Tuesday and were set for their second consecutive month of gains, driven by optimism around corporate earnings, while HSBC climbed after upbeat results and a share buyback offset news about its CEO's departure.

The FTSE 100 was up 0.4% as of 0715 GMT, hovering just below its all-time highs hit a day earlier. The index looked set to mark monthly gains of more than 2.5%.

HSBC Holdings gained 2.5% after the Asia-focussed bank reported better-than-expected pretax profit, announced $3 billion worth of share buybacks, which offset the announcement that its CEO Noel Quinn will retire.

Standard Chartered also rose 2.0%.

Limiting gains in the blue-chip index, however, insurer Prudential fell nearly 5% after its first-quarter results.

The mid-cap FTSE 250 edged up 0.2% to trade at a more than one-year high after it breached the 20,000 mark in the previous session.

The biggest boost came from Hargreaves Lansdown, which jumped 7.6% after the investment platform saw good momentum in April as clients invested at the start of the tax year to claim more benefits.

Global investors are anxiously waiting for the U.S. Federal Reserve's policy decision on Wednesday to see if the U.S. central bank turns more hawkish.

Meanwhile, prices in British shops rose at the slowest pace in more than two years this month, the British Retail Consortium said, adding to signs of easing inflation pressures that will be welcomed by the Bank of England.

(Reporting by Pranav Kashyap and Sruthi Shankar in Bengaluru; Editing by Varun H K)