Prior to 1999, Britain elected its MEPs by a system of first-past-the-post constituencies similar to those used for general elections, save that because the number of MEPs sent to Brussels/Strasbourg was much smaller, the constituencies were proportionately larger. Britain was the only country to do this, every other EEC/EU member state using various types of PR. When Blair got in in 1997 and during his early 'putting Britain at the heart of Europe' phase, this was replaced with the current system of a few very large constituencies electing multiple MEPs according to a party list PR.
What if Blair had kept the former method?
On the face of it this seems like a eurosceptic idea - "Sod the continental pansies with their sissy PR, FPTP is for men!" - but it would actually impair the formalised eurosceptic movement in the UK. There's no way in hell UKIP could make their 1999 electoral breakthrough under the old FPTP constituencies, meaning they would probably be reduced to a Conservative pressure group threatening to run spoiler candidates rather than their OTL success in eventually exceeding Labour's popular vote and matching their number of MEPs by 2009. Also, having a single local MEP people could recognise on telly and write to like their MP would probably make the EP seem much less distant and faceless to the British public. When the EP started passing unpopular legislation like the furore over the metric martyrs, the public response might be "I shall write to my MEP who sits in the EP and tell him to table a motion against it" rather than the OTL "hurl that distant ivory tower into the lake of burning sulphur!"
So, while it's a bit out of character for Blair - maybe he just gets persuaded it's too much of a radical constitutional change at the same time as the Scottish Parliament and Welsh Assembly and it gets shelved and then forgotten? - what if Britain stuck with the old FPTP constituencies? What would the euro-election results look like in 1999, 2004 and 2009 assuming politics in general proceeds along approximately the same pace?*
(*although this is a bit of a questionable butterfly net considering how important the European Constitution in 2004 and the Lisbon Treaty in 2009 were at times to British political discourse and how UKIP had an influence and pulpit it wouldn't have in TTL)