Both.
However parties can set their policies to appeal to a voter base - Labour since the days of Corbyn and to an extent Miliband have danced to the tune of their middle class left politician's and think tanks hence why they have basically handed Tories power for the last 10 years.
Im not deluded enough to think a switch to the centre would suddenly shake off the left tinted specs alot in the Labour party have but providing their policies appeal to the centre ground then thats as best as you can hope for.
You'll never get a proper labour party until someone like Dave the Plumber has any real say - what do former lawyers, academics etc. Know about the working class?
I’m sorry, but that really isn’t the history of the last two decades of the Labour Party.
What is it about New Labour that makes you think they went after working class support over middle class support?
What is it that makes you think Labour MPs haven’t been made up of lawyers, doctors, etc for the last while? It was Blair who reduced the unions’ power!
If parties set their policies only to appeal to a user base, that’s literally the whole definition of populism!