Free military-style workout session!

the_skint_minx

One for the masochists.

British Military Fitness do these training sessions in parks around the country - suitable for all levels of fitness, and I'm told that you don't get shouted at and the instructors aren't horrible to you or anything, but it is a vigourous workout using the techniques that the army use.

First session is free with no obligation. Check out https://www.britmilfit.com for classes in your area.

Beyond that, however, it's kind of expensive, about £6 for an hour's session if you go once a week (less if you commit to more sessions). My local leisure centre does a truly evil circuit training class for half that price.