There are two types of UPS on the market. The most affordable type is one that outputs a simulated sine wave in the AC component. The other type outputs a true sine wave in the AC component. There are arguments galore over which is best for a computer like the M1 Studio Max. True sine wave is exactly like what comes out of your mains but they are somewhat more expensive.
I own an M1 Studio Max and use an APC brand UPS that outputs a simulated sine wave. I’m in the U.S. so I don't what brands are available to you but here APC is very popular. Of course make sure you pick one that is compatible UK voltage and frequency. Here it’s 120 volts 60 cycles. I believe Europe is 240 volts 50 cycles?