Carrera Transit at
Halfords is a very good option. Hub gears make a lot of sense on a folding bike, more robust, less maintenance, easy up/down gear selection at any time ideal for urban traffic. Helps with the fold too. Yes a 3 speed hub doesn't give a huge gear range its something like 186% but the small wheels means the bike is relatively low geared anyway and not the ideal type of bike for fast gearing anyway. The trouble with derailleur gears on folding bikes is they are so close to the ground so pick up a lot of crap and they are easy to damage if you hit pavement etc. I think the classic folding bikes like Dawes Kingpin and Raleigh Twenty showed how hub gears were ideal for folding bikes and really derailleurs are less than ideal for this application.
Looking at the Tern its just a basic Tourney drivetrain but with cassette rather than freewheel. The Carrera Intercity seems a better folding bike at Halfords it is also 8 speed with V brakes but uses a higher quality Altus rear derailleur taken from Shimano's mountain bike range so it will operate better when dirty and cacked in mud, it has a greater spring force. I prefer the hub gear option to a derailleur on a folding bike but the intercity is a better derailleur based folding bike option.
I had a quick look at the decathlon folding bike range and most of the entry level models look awful to me but when you get to the btwin 900 at £499 that looks decent with 9 speeds and a Sora rear derailleur. I still prefer the Intercity as I think its a better configured design and cheaper but the btwin 900 is still a good option and looks very nice.