UK Stocks-Factors to watch on June 21

June 21 (Reuters) - Britain's FTSE 100 index is seen down by around 25 points on Tuesday, or 0.4 percent lower, according to financial bookmakers. * The UK blue chip index rose 3 percent on Monday to close at 6,204 points, its best single-day gain since February, after polls showed the campaign for Britain to remain in the EU gained ground. * BREXIT: Two opinion polls on Monday suggested support for Britain staying in the European Union had recovered some ground, but a third poll