trevHCS:
Not sure if theres an easy way to find the perfect tome to buy as it depends on mileage (hugely), warranty offered and brand of car. However the moment it comes off the forecourt its basically dropped its “new” status, VAT, car duty etc.However if I were buying second hand it would either be a KIA*, Toyota or Honda.
Kia wont hold its value as well but the warranty is very long so after 2 - 3 years it’ll have depreciated a fair bit and still well under warranty. Just be careful its not an older one has the controls are wrong way round. Some diesel KIAs have a timing chain not a belt so less worries later on.
Toyota and Honda will retain value bit will keep it for you too and as Juddian mentioned, they usually dont go wrong. Have you ever seen one on an RAC truck?
Nissan isnt bad and will keep value, but not as reliable as other two in my experience and according to my mechanic. Very expensive to fix but do come with timing chain.
Skoda, had one about 5 years old and wouldn’t touch another. There’s problems with the oil pickup pipe so if anyone used semi syth instead of fully synth (which most cars wont care too much about) then it storing expensive problems for future. Seem to be poorly spec’d for the money and all sorts of little things can go wrong. Very poor version of a VW.
Personally I’d not worry about deprecoation but more long term costs so things like timing chain can save tons of money long term and diesel engines just seem to last. Plus less likely to be owned by a boy racer.
Psst, if you want a 5 year old KIA Ceed for £9995 very good condition, fully depreciated, 2 careful-ish owners…luv juvley!
Was it a 1.8 20vt by any chance 
I’ve only ever had “older” cars although recently I looked at a new Vauxhall Insignia but the depreciation on it would have been a fair bit over the years