It's a tricky one
Problem is those AGRs have to go. Nuclear power stations have a design lifespan and whilst it can be extended there are limits. Hinkley Point B for example could have been extended a bit but ultimately the corrosion and graphite bricks warping in the core caused by a lifetime of ionising radiation was always going to be limiting. These are 2nd gen reactors, we learnt from them, it's time to move on.
France's Flamanville 3 was the prototype for the 3rd gen EPR design, expensive but informative. Hinkley Point C has gone better, especially the 2nd reactor but it's still basically a 2nd gen prototype. Sizewell C will be even easier to build but it's the last one for which the build is near certain. Whether they go on to build more depends whether politicians hold their nerve. These are long term projects that take longer than the lifetime of a parliament to reap the benefits from... Basically if we want this to happen there needs to be one hell of a grassroots pro-nuke lobby going on.
One alternative is to keep burning gas, which given peak oil in the North Sea was 2001 means either relying on unreliable partners, imports or a move back to "town gas". The UK lacks the storage the Germans do to stabilise this market, unless that is rebuilt I suspect it'll be a while until that market stabilises.
Another is to put a metric butt ton of investment into pumped storage. UK doesn't quite have the geography for this that Norway does so it'll cost a lot and take time to build. It's also energy agnostic, it can smooth out demand from anything.
Lastly you can insulate more. British buildings are still pretty useless in terms of dumping energy from the inside to out, especially all that dodgy 80s and 90s double glazing which past their service life and pretty useless to boot. Again, energy agnostic and saves money whatever you choose for generation. Previous attempts at this have flopped because it's not as fancy as a new infrastructure project, but it damn well works.
Frankly all the good options right now require mega project style investment, the do nothing option ain't gonna fly.