Last time when I travelled, I had 10 100 ml bottles in my clear plastic bag which I got from home.
When I got to security, they said the bag was just slightly oversized even though it is within the limits. The bag was too big dimension wise and had to bin one of my liquids.
I like to pack my liquids at home as I usually take a lot. Is there a set bag size UK airports follow?
One liter is the limit, as all airport and most airline websites in the EU will tell you, as well as the TSA site, (although they use the American way of notation.)
10 bottles of 100 ml will take more space than one liter, even when you have very efficient square bottles that just fit the bag, as the wall of the bottle will also take some space.
If you feel you really need to bring 10 bottles, make sure several (or all) are smaller than 100 ml. 75ml will likely do, but if you are only traveling for a week or two, you will likely not need even that.
Plastic bags in the UK are often sold with ‘one liter’ mentioned on the packaging. Only if you can not find one of those go for one where the measurements are the only indication and go for a smaller one, (not one that is slightly bigger.)
With full bags the security officers are more likely to measure the bags. They never measured my liquids bag, but with only one, or at most two, containers in, they do not do more than eyeball them. I have also used bags smaller by a huge margin and got away with that.