One thing Vidcapper and I agree on 100% is that the UK political system is geared around the 2 parties keeping their stranglehold on power.

Also, in our system, a centrist vote is seen as, and often *is*, more a protest vote than a solid endorsement of middle-ground politics. That's partly because they have to rely on policy 'scraps' that the main parties have little interest in.

Indeed, the problems with the term "centrist" is that it means something different to everybody. I've been calling myself a centrist on here since before being a centrist was cool, but I've usually prefaced it by calling myself the "wrong kind of centrist", due to being economically on the left, in favour of greater nationalisation and a generous yet trampoline-like welfare system, whilst being, for lack of a better term, more "conservative" on social issues. A centrist party of that sort would gain great support if it ever were to strongly emerge, as there are quite a lot of people who would fit more into that base whose views aren't matched on a UK-wide basis by any mainstream party (perhaps a few individuals who would be classed as "Blue Labour" or "Red Tory", but no party machine).

Of course, if such a party were to emerge, it would face a two-pronged attack, from the right-leaning traditional media for its economic policies, and from the left-leaning media and Twitterati for its social policies - if any member of said movement was to so much as let off an ill-timed fart, the entire media landscape would pounce and tar the entire movement with the same brush, killing it off straight away.

If they have so little interest in those ‘scraps”, why do they steal so many of them?

Quite similar to European style 'Christian democracy' then, if I understand that philosophy correctly. Whose parties makes up a large part of the European EPP, another reason why it's quite strange that the UK doesn't have a popular party that matches it, if it's popular in so many other countries, what has gone differently here? You might guess the Tories should have that niche, but they've lurched further right than they should have and certainly don't have an economic-left policy.

There was an article on CapX yesterday which revealed that it is the economically leftist, socially conservative are the group that feel the least represented by the current parties

, so there is a gap for such a party to break through. The closest party with any real chance of delivering on it at the moment are, quite pertinently enough, the SDP, or at least its current incarnation of it. I've been following their progress with great interest over the last few months since they gained an MEP, and I've seen quite a few people that I follow on Twitter joining the party recently. They revealed their policy platform a few days ago, and I'll happily admit that there is a great deal of it that I would agree with.
The only sticky wicket however is that they are firmly pro-Brexit: their MEP defected from Ukip, and some of their new membership has come from that party (although quite a few of the party that I follow that joined came from the "blue" wing of Labour, including quite a few that voted Remain). I doubt they're going to make any real gains any time soon, but as far as ecolsocir parties go, they're perhaps the only real prospect around.