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* European markets rise, set for 5th day of gains
* Voting starts in Britain's European Union referendum
* Tesco rises after reporting sales growth
By Sudip Kar-Gupta
LONDON, June 23 (Reuters) - European shares advanced on Thursday as firmer copper prices lifted mining stocks, while expectations among financial investors that Britain would vote to stay in the European Union also supported markets.
The pan-European STOXX 600 and the FTSEurofirst 300 were up by 0.3 percent. They were set for their fifth straight day of gains and both were around a two-week high.
Supermarket Tesco outperformed the broader market with a 1.9 percent rise after reporting a second successive quarter of UK underlying sales growth.
Mining stocks such as Glencore also advanced as London copper prices neared two-week highs.
Voting got underway in Britain's referendum on EU membership with most opinion polls putting the "Leave" and "Remain" camps neck-and-neck.
Bookmakers, however, have consistently given a greater probability towards Britain staying in the bloc rather than leaving in a "Brexit" scenario. The result is due on Friday
Britain's FTSE 100 equity index was up 0.5 percent, while sterling also rose on currency markets.
"Regarding Brexit, I think it's a craps shoot, but 'Remain' will probably eke out a small win," said Emanuel Arbib, chief executive of Integrated Asset Management.
Richard Griffiths, associate director at Berkeley Futures, also said most investors were backing a victory for the 'Remain' camp, but added markets could fall by 7-12 percent in early trading on Friday if the 'Leave' camp won. (Editing by Richard Balmforth)