Are you certain there's no chance of you being able to buy in the next few years, even if it means moving area?
With £50k, that could be a really good deposit on a 2/3 bedroom house in many parts of the country, that you could get a mortgage for, even if you earn NMW as long as you work full time, so don't completely dismiss that as an idea, especially if your medium term plan could be to buy when your DC have grown and you only need a small property for you, as this would be security for you when you're older.
What are your current circumstances, age, any DC and their ages, any chance of retraining, any ties to where you live now? What are your pension arrangements?
If you invest, the money is likely to grow faster than a savings account, but you'll need to ride out ups and downs in the stock market - what you need to avoid is having to take money out when the market is down, as that crystallises the loss.
But on £50k, it's going to be several years before it grows significantly, even if you invest it all and it grows well so while you don't want to just fritter it away, if you're currently struggling to make ends meet, it might be a worthwhile use of the money for some of it to (carefully, ie top up your income by a few hundred pounds a month, not spend it all on big cars, fancy holidays and high end gadgets within the year) make your life easier over the next few years. No point living hand to mouth with £50k available to you.
Something else that is relevant is that, if you're genuinely short of money, as in you don't have enough for a decent basic standard of living, if you didn't have the £50k, assuming you have DC, you are likely to be entitled to universal credit to top up your income and help with childcare costs if you need this, so you should spend the money on living expenses because when it reduces to under £16k, you'll then be entitled to help.
Could you use some of the money to invest in a career, retrain so you can earn a better salary in the future? What about buying a decent car, so you won't have car expenses or worry about keeping a banger on the road for a while? Or driving lessons if you can't currently drive and this would open up better paid work to you?
But assuming you don't plan to spend a lot of it as suggested above over the next year or two, you have a £20k annual ISA allowance so what you could do is put £20k in a S&S ISA before the end of this tax year, another £20k in next tax year and keep the other £10k in cash in the highest paying instant access savings account you can find. That's probably the best use of the money in terms of making it grow as much as possible while you decide what to do with it.
Sorry, that was long but it's not a straightforward question and I've still probably missed something (eg pensions) 