Can of worms asking for recommendations for a rum!
As above, I have my own rum distillery, but won’t be recommending my own stuff as it’s against forum rules ;)
It’s important to know what your Dad usually drinks – is he a spirits drinker? Also, is he diabetic? Most of the rums recommended above are sweetened, some heavily (hence why they’re so ‘smooth’, ‘moreish’, and bad hangover inducing.
The safe bet is probably The Duppy Share at around £26. You can pick it up in Morrisons or Asda, and through Amazon: https://www.amazon.co.uk/Duppy-Share-Golden-Caribbean-Rum/dp/B00N1YI01I/ref=sr_1_5 It’s a very easy going blend of Caribbean rums from Barbados and Jamaica and is a great introduction to ‘proper’ rums (not the sugared Diplomatico, Flor de Cana, Plantation etc.) and it’s an absolute steal for the price.
Appleton Estate 12 is nice, but quite woody with lots of banana so not sure if that would suit your Dad.
Mount Gay XO is great but over your budget, so the Mount Gay Black Barrel looks a good alternative (but never tried it myself).
The above depends on his taste though. If he’s got a sweet tooth then pick any of the recommendations from others, he’ll likely enjoy them.
If in doubt, check out the reviews at The Fat Rum Pirate https://thefatrumpirate.com/rum-reviews