If you £200k into a 5-year fixed ISA you could get a rate of 2.3% p.a., tax free.
(Source:
https://www.moneysavingexpert.com/savings/best-cash-isa/ )
So that's an income of £4600 per year.
£650 per month in rent will bring you in £7800 gross but, in order to work out your net gain, you'd need to knock off:
(a) the costs of maintaining the property ;
(b) your letting agent's fees (if relevant) ;
(c) the cost of landlord's insurance ;
(d) loss of revenue when the property is unoccupied between tenancies ; and
(e) the tax on your profit.
You can get an idea of what a letting agent might charge here:
https://www.simplybusiness.co.uk/knowledge/articles/2017/01/letting-agent-fees-for-landlords-a-quick-start-guide/
Guidance on paying tax can be found here:
https://www.gov.uk/renting-out-a-property/paying-tax
I'll leave you to do the rest of the sums. I suspect though that you'll find that, at first glance, you can earn slightly more from buying (and then renting out) the house than you can from a safe investment, such as an ISA. However you'll then have the worry of possibly having to pay for unexpected repairs, concerns about whether there might be lengthy periods with no tenant and the uncertainty of not knowing whether your tenants will keep paying the rent on time (plus the potential difficulties in getting them out if they don't).