It is impossible to answer such question particularly, but it is possible to give generic guidelines.
First you must determine your consumption requirements. In my case it's mostly internet data, about 100 MB a day, but everyone has individual requirements. Than you check the available bundles/packages on operators, for both internal and roaming. Usually, by higher consumption, buying local SIM card make more sense, because roaming tariffs are very expensive, and no, removing roaming fees will likely change nothing, because the basic price will be based on the 'local' prices, still very expensive compared to bundles/packages.
But by moderate consumption and/or visiting countries where prices are extreme, roaming bundles might be cheaper than local cards. For example, in german ALDI you get (currently) 500 MB mobile internet in EU and Schweiz for 5 Euro for 1 week, and the cheapest SIM card in Schweiz costs 20 CHF, and usually for 15 CHF you get 1 GB data.
Because local cards you can buy only in particular country, you will always need SIM card for country where you start, so you should start your analysis with UK. By ALDI, you can get 1,5 GB internal internet for 10 Euro, so you can cover it with starter pack (13 Euro). So if you need as much, and the roaming package from UK would cost you more than 13 Euro, buying German SIM would be cheaper.
If the differences are a few Euro, you can spare yourself the problem of buying SIMs. It's another factor to consider.