Depends on lots of things. Is the 50k part of a portfolio, how long can you leave it untouched, do you need short notice access, what risk level is acceptable? I'm sure you know all this stuff but PBs return 1% tax free on average at 0 risk. Savings accounts seem to be .35-0.5%
A bundle of funds - mainly trackers to keep charges down - Dow/FTSE/Europe/Emerging markets/Tech type of thing? Depends where you think things are heading over your planned timescale.
Something like a Blackstone bond fund? Boring but steady.
A bundle of income shares- re-investing income - or an income fund - although a few of the key UK income shares have drifted down in value so an income/growth fund might be a better bet.
If you want to go off piste there are some art works that you could enjoy for a while that look like safe bets (but purchase and sales charges can be eye-watering). Markets tend to be a bit 'fashionable' though.
TBH 50k in PBs looks quite attractive given all the short/medium term uncertainty and other interest rates.