Standard Freeview set-top boxes don't have a built-in RF modulator, which is what you need for an output that can be fed to a TV's aerial socket. In the early days of Freeview some (more expensive) boxes did have them but I've not seen one now for well over a decade. A quick look on both Amazon on eBay fails to find any. (You can purchase separate RF modulator units, which go in between a regular Freeview box and the aerial socket, but they generally cost far more than the box does anyway).
However if you work out how to switch the TV set to display a signal from an external source (via the RCA input sockets), there's still a way around the problem. [This isn't just a theoretical idea of mine. It's something that I've done myself and also set up for a friend]]. The trick is to buy a 'Scart-to-phono' cable. It's unusual to find anything cheap in Maplin's but it seems that you're in luck with that particular cable:
http://www.maplin.co.uk/p/scart-to-3-phono-plugs-with-inout-switch-15m-l99ba
So you plug the Scart plug into a Freeview box. (If there's an In/Out switch on the Scart plug, set it to 'Out'). The yellow (composite video) plug goes into the appropriate socket on the telly. You then use either of the other two plugs (red or white) to go into the sound socket on the telly (unless, unusually, it supports stereo). You'll obviously lose half of your stereo signal but you'll find that it won't matter because the channel separation used for TV broadcasting isn't very wide. (The only time I ever noticed a problem was when listening to repeats of panel shows, on Radio 4 Extra, which had originally been broadcast in the early days of stereo radio. They were recorded with very wide channel separation and half the panellists disappeared when one stereo channel was missing).
So, in summary, you need:
(a) a cheap Freeview box (around twenty quid in larger supermarkets or Argos - or £5 to £10 in a charity shop, such as a BHF 'Electrical & Furniture' outlet ;
(b) a Scart-to-phono cable (a quid from Maplin's) ; and
(c) to know how to switch the telly to accept a signal from an external source. (In some cases you simply select 'Channel 0'. With others you need the remote control to find a 'Source' option).