Mass migration by Labour was for two reasons:
1. The majority of immigrants from third-world countries will vote Labour and the senior Labour luvies hate the British people, our culture and history and this was the most effective way to destroy it. Also all immigrants from EU countries are pro-EU for obvious reasons, and for those outside, they don't care. Tony BLair also personally benefitted from this and the human rights act that he signed up to, though his wife's increased earnings.
2. It suited the Labour government to drive down wage costs and to stop UK workers from working, so they then became clients of the state. The natural Tory voters them would then not vote for the beastly Tories who would cut their benefits. Also by driving down industry costs, inflation would stay low, interest rates low (too low, which caused the housing bubble), so they could raise taxes without people feeling too badly off and borrow lots of money to make them feel even better. Deregulated the banks and allowed them to do whatever they liked as long as they made huge profits, so Labour got more tax money to spend. This is how they managed to get 3 terms in office and almost a fourth term.
Labour also gerrymandered the boundaries for MPs to their advantage, which the LibDems are currently trying to stop being corrected, by renegading over their agreement, over the referendum they got over the voting system in return for supporting this. They are putting party over ethics and they are openly courting Labour-Lib Government after the next election.
Labour has always been much more mercenary about changing things while in power to their advantage to stay in power and every Labour Government from the 1920's onwards has ALWAYS run out of other people's money. This is when their merry-go-round has stopped and they have been voted out, for the Tories to pick up the mess, we go through years of pain and as soon as they have fixed the problems, we have another 3 labour terms to start the cycle all over again.
Most Bulgarians and Romanians (and Ukrainians) are already here, via Poland, where if you worked for 2 years there (especially as a low paid agricultural worker), you can / could (not sure if this easy entry route still exists) get Polish nationality which opened the whole of the EU to you. This is what happened in large numbers, due to Polish mass migration to the UK, so they had a labour shortage. There will be a small influx from those countries and they may well be many who will be here for easy pickings, rather than the hard work Polish route.
Reading the comments section on the DT page is very interesting on why many people professional people have left or are emigrating from the UK.
http://www.telegraph.co.uk/expat/9667069/The-new-brain-drain-and-who-can-blame-them.html