That is a Wylex Standard.
You can get push-in MCBs to replace the old fuses. They cost about £7 new or about £4 on fleabay for used ones. the older model, with push-buttons instead of the switch, are about £2.50 on fleabay. You must get plastic shields to fit, with them.
to fit them you have to turn off the main switch and test for dead. You do not have to take off the CU casing, but after pulling out the fuses you have to unscrew the plastic shield behind, and replace with the new one of the same colour from the replacement MCB (they are sized to fit and not interchangeable). then push in the MCB. Take out and replace the MCBs one at a time, do not take them all out together (this reduces the risk that you might accidentally mix them up)
when you take out the plastic shield, a copper busbar is exposed. this is live if the main switch is on, but dead when the main switch is off. You do not need to touch it anyway.
you can pay a qualified electrician to do this, as it is notifiable work.
However I have reason to believe that approx 0.0000% of these swaps are notified.
p.s. if you get an electrician in, it would make more sense to have the old CU replaced with a modern one, and the old stuff tidied away. Make sure he is a member of a self-certification scheme - ask for evidence before giving him the job.
p.p.s. the 45A MCB you already have is probably for an electric cooker or electric shower. It is probably too high a load for that model of CU, so if it is still in use, you ought to get a new CU of sufficient capacity.
p.p.p.s. you ought to have circuit labels above every fuse to say what they do. you can make your own with white vinyl tape and a permanent marker.
