Right, I'm back home now, with all my shopping put away ;-)
AC Computer Warehouse is excellent
https://accomputerwarehouse.com/product-category/cheap-refurbished-laptops-uk/
but their cheapest laptop at the moment with an SSD (solid state drive), which I suggest that you should definitely be looking for nowadays, is £249. It's still an excellent buy though.
When I was looking for a laptop myself, I couldn't find anything to suit my needs from that firm, so I was forced to look elsewhere. I eventually bought from this seller
https://www.ebay.co.uk/sch/PC-Laptops-Netbooks/177/m.html?_nkw=&_armrs=1&_ipg=&_from=&_ssn=kelsus-tm
which I consider to be excellent. (The condition of very laptop offered for sale is often described exactly, down to small little details, such as 'missing Windows sticker').
Out of that lot, and with your very limited needs, this is what I recommend. It's excellent value, at just £130:
https://www.ebay.co.uk/itm/184869041644?hash=item2b0b0db5ec:g:RNgAAOSwkztgRlRH
NB: I'm assuming that you store all of your music files on a portable drive or, perhaps, on memory sticks. If you want to store them on the laptop itself, you're likely to need a bigger SSD. In that case, my recommendation would switch to this (but it will set you back two hundred quid more):
https://www.ebay.co.uk/itm/203479617037?hash=item2f60548e0d:g:LEoAAOSwtZ1gp5hg