Centrist is the wrong term, this is not about right vs left. I would argue it is more about conservative vs liberal, where conservative means set in their ways, traditional, authoritarian, and liberal means open, willing to accept other ways and democratic.
While this may seem obvious about the conservative party, it also applies to the labour party. Corbyn and Momentum are not part of a liberal left (or even anarcho as Gulley has tried to imply a couple of times), but of a conservative, authoritarian (and marxist) left. Despite the talks of 'members direct policy' labour continue to ignore a large part (maybe even a majority) of their members and voters. Corbyn continues to ignore party opinion while pressing ahead with a hard Brexit. He doesn't want a second referendum because 'he knows what the people want'. That's not democratic! He continues to push for a new GE, because he values being in power above everything else. That is definitively not 'anarcho'.
I do see that there is a need for a new party, and for both labour and the conservatives to split. But it would be a party formed more of the liberal, pro-european, anti-nationalist parts of both parties, not the 'centrists' ones. If the lib dems hadn't lost so much of their political influence, you could see them offering a good middle ground for new influx. I can see them as being a bit too market liberal for some, but I'm not sure why there haven't been at least a few changeovers.