Can neighbours refuse our builders access to paint exterior wall on their side of property.
Do you know the revenant section of law on this?

No further action needed. All sorted via our builders.

So what was the bottom line?
Did you find out the relevant regulation that will allow you to enter your neighbours property for maintenance?

I thought someone had posted something but next time I looked it had disappeared. I would be very surprised if neighbours can refuse access, in particularly because alot of houses are built 0.5m from the boundary with no fence along the boundary where the house is sited. (Does that read write?).

The neighbours can't refuse access but conditions can be applied (time, damage liability or/and compensation (I think) etc.) but I don't know the details or the PTK paragraph that refers.
If it gets silly the court will expect people to be reasonable and will make a judgement based on what they think would be the reasonablely neighbourly thing to do.
Rather than maintenance the usual problems are with over hanging trees and the ownership of any fruit thereon. And the cutting back of said trees.

Ever since we moved to our house the female half of the couple next door has never been friendly with either of us, especially me! Everybody else ... no problem, especially the fantastic team of builders, plumbers, electricians, window/door fitters we've employed past four years.
I think the neighbours will regret being "silly" because their outdoor kitchen is built right up to the boundary so if they need to replace the roof guttering they'd only be able to access it from our side! Of course I've no intention of reverting to the same behaviour but I'll remind them their outdoor kitchen shouldn't be built right up to the boundary, with the guttering just 1cm from the boundary!
At the end of the day ..... I learnt working for the NHS .... sometimes you can't win an argument so it's best to grovel and apologise, letting them think they've won!