Taking forever to dry indicates low porosity. Chemically treating hair can alter the porosity...but doesn't automatically mean high porosity. Does your hair seem to take a while to get wet? Do some products (oil, for example) tend to just sit on your hair? Run your fingers up a strand - is it smooth? Do a float test - place hair in a cup of room temperature water, does it float? That all also indicates low porosity.
A very good answer regarding frizz is here: Help! Dry, frizzy hair. What could it be? - CurlTalk
I struggle with the exact same problem. You said UK right? It's very wet over there? I'm thinking the majority of your problem is probably the wet air so getting something for your hair to battle humid conditions would be a start. I personally stay away from products with glycerin and it seems to help a lot. Vegetable glycerin is ok for some reason on my hair, but glycerin in general... I skip it. Also i've been doing Agave Nectar rinses (my hair is long and thick so I use 2tsp. to 2 cups water) as my final rinse and it's been keeping my frizz down also. I don't rinse it out, I just scrunch it in my hair gently and leave it in. I live in Texas and near the gulf so it's humid here a lot, with dew points in the upper 60's. Now that the season in changing (which might be the case where you are now) my hair is doing much better with the frizz without a lot of work due to the lower dew points in the 54 range. Hope I didn't confuse you too much, those are things that I do. The curl predictor tool works great for telling you the type of products you need to seek out for your area and hair type. ^_^
You didn't mention if you use a low poo or anything to clarify your hair. If this is a more recent thing, it could be due to buildup on your hair.