Wenchy, it's not some sort of irrational blind loyalty, but a recognition that certain parties represent certain core voters and ideologies that aren't going to change overnight. Unless they're incredibly naive, people don't go out and vote BNP based on the strength of their election manifesto, because they know their hidden agenda is the destruction of democracy and civil liberties. As we have seen with New Labour, for all the Tory-esque policies on crime and foreign affairs, they have still pursued the core Labour agenda of tax and spend and the welfare state. Likewise, with the Tories, they can't be trusted not to look after the rich and the English home counties at the expense of the rest of the UK, with all the division, despondency and crime that accompanies.
As far as I am concerned, the party who will look after my financial interests are Labour, but being ideologically libertarian I can't bring myself to vote for a party that treats its own citizens like naughty children, who need to be told what's best, put on a database and spied on.
Ahh but you see that arguement makes sense. Many labour voters don't. It isn't an ideological choice because labour best represent them, clearly labour does represent you. However, when it doesn't why continue to vote for them simply because that is what you have always done?
They may not have considered it in terms of core ideologies, but that is certainly what it boils down to Wenchy. As working class folk, they feel connected to - and trust - the Labour party. They have always voted labour, so why would they want to change?
YVMV but I've never met anyone who "votes Labour cos I've always voted Labour" who would be better represented by another party.