I have been told that the cheap pine disinfectant that you can get in pound shops works extremely well. Pour or spray liberally, leave for a few minutes then scrub and rinse.
Just bear in mind what plants you have next to the patio - they will be killed by the run-off. I've never used chemicals because of this - use a hired pressure-washer for about £16 per day from a hire shop (though not whilst the water restrictions are in place)