The pound prolongs its upward move against the greenback into a fourth straight day today, extending the bullish 100-pips opening gap above 1.46 handle in the late-Asian trades.GBP/USD climbs almost 3 big figures from Friday’s closeCurrently, GBP/USD now jumps 1.72% to 1.4606, easing slightly from fresh nine-day highs reached at 1.4623 last hour. The cable keeps pushing higher as bulls aim to surpass the 200-DMA barrier for further upside as odds for Britain to remain in the EU appear to have increased over the weekend.The latest Brexit opinion polls show votes shifting in favour of the ‘Remain’ campaign as we step into the EU referendum week. BMG phone poll has 'Remain' leading by over 7 points, YouGov: 43% Leave, 44% Stay, 9% Undecided, Opinium: 44% Leave, 44% Stay, Survation: 42% Leave, 45% Stay, 13% Undecided.Markets will continue to closely monitor the development surrounding the British vote on EU’s membership, which scheduled on June 23rd, Thursday. The EU referendum is expected to be the biggest market moving event for the weeks to come, and it is likely to overshadow most major economic news and Fed Yellen’s testimony due later this week.GBP/USD Levels to consider The pair has an immediate resistance at 1.4644 (200-DMA), above which 1.4700 (round number) would be tested. On the flip side, support is seen at 1.4500 (round figure) below that at 1.4475/50 (50-DMA/ psychological levels).