It'd be about £400/month where I am as well, and I'm guessing you're not in London/Cambridge/Oxford.
Also since you're in the UK don't forget about rates (local property taxes that businesses pay in the UK). Once you're beyond a certain size this tax will jump from £50 a month to over £1000.
In London it's more like 600-700 for good quality places in a co-working space (Wework or similar), up to 1k+ for particularly central locations. But then if you can afford the salaries here, the 300-400/month increase per team member compared to a desk in a co-working space doesn't need to cause a particularly big performance bump to be worth it.
Also since you're in the UK don't forget about rates (local property taxes that businesses pay in the UK). Once you're beyond a certain size this tax will jump from £50 a month to over £1000.