Hi, welcome to GoY, if you didn't put a heavy duty weed suppressing membrane down before you laid the block paving, then the only thing you can do is keep using weed killer, and moss killer, or use a hoe regularly, Derek.

You can buy a tool to rake out the old sand, a long-handled wire brush and then renew with a sand-based product which is supposed to contain a chemical to stop the growth of moss and weeds between the blocks. B and Q and DIY outlets sell it. Perhaps some others may have used it with some success?

I fear "supposed " is the operative word though. If the original sand was properly sealed it would take ages to brush it out unless its only a small area. Ours wasn't supposed to get moss and weeds but it does and I fear something like Pathclear or hypochlorite is going to be the only solution and it will need doing annually. You can buy it in fairly large containers more cheaply than using domestic bleach.

our neighbour uses Pathclear twice a year on his.

Yup, Pathclear; most effective if applied April or May, keeps it weed and moss free for up to 3 months, sometimes a bit longer, so twice a year should work well. Be careful of run off though, I use a watering can with a very fine rose fitted on it and try to just water the gaps between the stones

I love the affect of green fuzzy moss growing between the pavers. If you want it gone, spray a high concentrate salt solution with soap. Those weed membranes don't work and look awful. Weeds grow through them. They are a waste of money and a royal pain to deal with.