Just seen these Thomas the Tank Engine carriages in Home Bargains for only £2.99 each!
They are die-cast metal carriages, with magnets on, for use with the Thomas Take Along train set (although they could be played with standalone, too).
The store near me had 3 types:
~ Green - Sodor Log Loader (with log release functionality);
~ Purple - Smelter Shed Cargo Car (with glowing cargo);
~ Red - Didn't catch the name of this one, but it contains rocks (with rotating and disappearing rocks)
Also, as found by Scoutfinch, some Home Bargains' have double packs for the same price - "Annie & Clarabel" and "Iron Bert & Iron 'Arry".
RRP was stated to be £12.99 (Edit: seems the 'real' RRP is more like a fiver, but still... not a bad saving :))