>>> "I have an iPhone if that’s any help. Can I charge laptop via its battery?"
Nope, sorry! A laptop requires a LOT more power than a mobile phone does!
'Universal' laptop chargers are sold but, alas, not by Argos. (If you can find one, you need to ensure that it's power rating is up to wat's needed by your laptop. Some others might not be up to the job). Your best chance of finding something suitable for your needs on the High Street is probably in Currys:
https://www.currys.co.uk/products/logik-lpdell16-dell-laptop-power-adapter-10142593.html
(NB: Not everything on the Currys website is available in their stores. Enter your postcode on that page, and then change 'Delivery' to 'Collection', to check availability near to you).
Otherwise you'll probably need to look for something with rapid delivery on Amazon. If you do so though, you'll need to take great care to ensure complete compatibility with your laptop. (There are a LOT of different plug types and, as I've already mentioned, not every charger will necessarily be powerful enough for the job. If you buy one with too low a power rating, it could overheat and possibly catch fire).