Where are you living at the moment? Are you in a rented property. It's just if you are, then a great way to save money would be to buy whatever 200K gets you. Live there (doesn't have to be your forever home) and save on your rent as you will have no rent or mortgage to pay. Also you wont have to deal with the insecurity of the rental market.
Would this work - how much would you save on your rent (which would be extra income in your pocket instead. So not increasing your income but lowering your costs).
If you are living at home and want to stay there for the next 10 years then don't become a landlord. It's lots of work, problem tenants and when you sell you will pay GCT (the tax free allowance for this has been reduced dramatically in recent years)
Do what others have said - stocks and shares ISA each year 20K (although this might change with upcoming budget). Rest in best rate of savings account you can find. They are always changing so try money saving expert for best rates.
An example for you - I have put £20,000 into a stocks and shares ISA about 2 weeks ago plus £8,000 into a GIA (general investment account) and the value of £28K two weeks ago is now £28650 ish. (I reckon people are piling money in before the budget) However you do need to accept it can go up and down and not lose your nerve and sell in a panic if it drops for a while.
You don't want to make any more than £3K in gains per tax year at the moment on any GIA's as you will get taxed (also this tax free allowance subject to change in this years budget).
If you don't want to buy a property to save on rent (no reason why you can't live in a bedsit if that is all you can afford) then I'd use up my ISA allowance each year. Put say £10K into a GIA so any gains are tax free. The rest put into savings accounts and transfer them to ISA when the tax year refreshes.
I recently put 75K into various pots. 28K as mentioned above. 20K into a 1 year fixed bond with a bs at 4.5% interest and 17K into a BOE tracker at 4.55%, 4K set aside for unexpected vet fees in an easy access bank account with 3.9% interest and the rest into my pension (2 years worth at £2880). Obviously pension would not be relevant for you by sounds of it. I'm retired so max I can put in is £2880 pa. The figure is much higher if you are working.
Anyway it's a nice problem to have. Good luck
P.S. So the funds are invested so they all have different flexibility and availably. The pension is not available till I'm 55 (I'm retired already but under 55). The BOE tracker is an instant access account so I can freely use up this money as I need it. The 1 year fixed is as it sounds - not accessible for the year but as rates are predicted to drop I wanted to lock this in. The ISA's/GIA's can be sold at any time although it takes about a week for funds to come through but you want to do this at a good time in terms of financial planning so you shouldn't be relying on this money as instant access. Also be aware that some bank/bs accounts won't let you get money out at weekends for example and some will let you take them out 7 days per week. I learned that when my dog got sick at the weekend and needed emergency surgery.