Are The Lib Dems trying to replace Labour?

I was thinking about this over the last couple of days, but are the Lib Dems trying to replace Labour?

As in of the three main parties there is one Conservative party and two progressive parties (the Lib Dems and Labour). Now since WW2 due to workers rights, trade unions and socialist doctrine Labour have always been the party of choice for progressives, whilst the Liberals have been a small party which are Liberally progressive but not socialistically progressive.

Now Socialism means less. Trade Unions are demising, Labour have taken a step towards the centre and the word 'socialism' is never brought up by main-stream politicians any longer.

Whilst this has happened the Lib Dems have joined the SDP and slowly but surely added a couple of more populist socialist ideals to their manifesto. Suddenly we have Labour who are probably are still democratic socialist but with a lot of liberal ideals, then we have the Lib Dems, still liberal but with a couple socialist ideals.

It seems almost like the Lib Dems are trying to capitalise on dissatisfaction with the current government to get progressives to vote Lib Dem rather than Labour. It seems to me that they perhaps want a two party system with a Liberal party and a Conservative party rather than a Socialist party and a Conservative party.

Thoughts?