I'd imagine most libertarian are likely to think that both the Democrat Party in the US & the Labour Party in in Britain to be socialist, but I'm wondering if its ever its ever occurred to libertarians that there are in fact socialists who believe neither the Democrat Party nor the Labour Party are truly socialist.

Okay both parties are what could be described as social-democrat which is a political ideology which has evolved from socialism, but to most hardcore socialists social-democrats are sell outs, because I guess social-democrats don't want a wholesale transition from a mixed market economy to a purely socialist economy.