David you can apply for VAT registration any time before the threshold, that goes without saying, course you don’t claim and you don’t charge VAT if your not registered.
But the original post is talking about being VAT registered and VAT is a tax for the man in the street only, it is not in any way a tax on business.
You can either interpret it the correct way or the wrong way it’s your choice.

Ewan,
You seem to be struggling with the implications to your business of going VAT registered if dont need to.
Let me try and break it down for you -
If you register for VAT
all your customers will have to be charged VAT...thats both your residential and commercial customers.
So, now we've established this - lets look at the next step
What can your business reclaim now you're VAT registered?Window cleaning is 'labour intensive' and has few overheads. So you've got some fuel, some scrim, new rubbers or poles, the odd brush.
So your 'reclaimable VAT' each quarter is going to be very low. But your 'VATable income' is going to be relatively high.
You now have two choices - 1. Absorb the VAT into your current prices (effectively reducing your price by 17.5%)
2. Put your prices up across the board by 17.5% to cover the new tax you have voluntarily agreed to pay HMRC.
If you dont have to go VAT (because your turnover is below the threshold) and your business cannot reclaim more than it pays, there is no advantage doing it.
It will end up costing
YOUR BUSINESS money. and thats leaving aside the extra burden of producing a VAT return each quarter!