Our patio is tiled and weeds grow along the joins.

As with most paving, it seems there was no geotextile membrane laid underneath, so weed growth between the cracks will be a problem every Spring. Suggest you buy some Pathclear or other make of Path Weed Control and water it onto the cracks every spring, following the directions on packs to the letter.

I put down a new patio a couple of years back and despite using a membrane under the patio i still get weeds. Rather than growing from under the patio they seed themselves in the cracks.
I am not one to be defeated by a few weeds so every year as soon the new growth starts appearing and the weather dries up a bit i go over the cracks with a weed killer, it sure beats getting down on your hands and knees to pull the stuff out. I've tried a couple of different products but to be honest I've found Roundup works the best as it kills right down to the root so the whole weed, from root to tip just shrivels up and dies.
I've also found it a good idea to repeat the process at the end of the summer.
Good luck Mervyn!!