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* FTSE 100, FTSE 250 up 0.3% each

June 5 (Reuters) - British equities opened on a positive note Wednesday, buoyed by weaker-than-expected U.S. labour data which fuelled expectations of a rate cut in September, while investors awaited the European Central Bank's interest rate decision on Thursday.

The blue-chip FTSE 100 gained 0.3% by 0722 GMT, after two sessions of declines. The mid-cap FTSE 250 also edged up 0.3% to 20,780.37 points.

Investors cheered signs of cooling in the U.S. labour market, where data revealed job openings plunged to their lowest in over three years, reinforcing predictions of a rate cut by the Federal Reserve in September.

Spirits were also lifted by the anticipation of a 25 basis point cut by the ECB, which convenes Thursday.

Among individual stocks, Paragon Banking was the top gainer on the mid-cap index with a 9.1% jump after the lender reported its half-year results.

WH Smith gained 3.2% after the British retailer reported its results for the 13 weeks ended June 1.

B&M was the top loser on the FTSE 100 with a 3.2% drop after the discount chain reported its preliminary full-year results. (Reporting by Pranav Kashyap in Bengaluru)