Great job OP - you've made amazing quick changes that will loosen your budget up for the future.
A bunch of you posting in this thread have no idea what you're on about.
There are many parts of Manchester where biking is downright dangerous. Add in to that the fact that OP's DP would be doing so after a long shift at variable hours. Plus, as a few saner souls have noted above, it's hardly like cycling is cost-free: you need to buy a reasonable bike, pray it doesn't get stolen, and not many workplaces have shower facilities where the OP's DP could get changed and fresh for work. Biking is not a universal solution FFS. And there are many, many places where car insurance is that high for a young male - which explains why it went down when OP added her name to it.
I wouldn't begrudge OP's DP (who is doing long shifts) the cost of a gym either, though it's great he found a cheaper place. It's a relatively low cost compared to the other expenditures, and it made much more sense to find a way to economise on the huge and disproportionate car insurance costs.
Free weights at home take up space and cost money. If he's going to switch to that, better to do so in, say, March, when all the people who got them for Christmas end up putting them on Gumtree.
Good luck OP, and hope you're able to find a cheaper place once your lease is approaching its end. Maybe even in an area where car insurance rates are less.