Further to this - the idea that floating/non-voters are generally "moderates," and that in order to win them over you must "appeal to the centre," is false.
In my experience, these people have not disengaged from politics because the options on offer are too radical; it is because they are NOT RADICAL ENOUGH.
They are not looking for a slightly different flavour of the establishment. They want an actual alternative, and their appetite is increasingly radical as the country around us continues to deteriorate.
I have spoken at dozens of Restore Britain branch meetings over the last 8 months, and I always make a point of asking those present to raise their hands if they have never been to a political meeting before. Every time, upwards of 80% of the room does so.
These are people who have spent years feeling that nobody represents them, and who are now engaging in politics for the first time because they finally see a party that will actually fight for their interests.
The great untapped electoral constituency in Britain is not the moderate centre. It is the millions of politically disillusioned Britons who have given up on the system in its entirety.