If you are self employed its a waste of money, because you have to prove your wage and the time you have to wait can be up to 3 months, plus lots of insurance will not cover SE (read the small print)
If you are Ltd you can get paid sick pay, see the government web site, if you get insurance (based on being employed) it is paid out sooner .
Best place to look is with the company you have your public liability insurance with, as they might have an add on to your policy which could cost you less.