At todays prices £5k to £6k for the 5 year old Avenisis looks about right.

The Avensis and i40 should have more room inside than the Qashqai - boot space and rear leg room, the i40 maybe a shade more? Both have 5 years warranties and Toyota have an excellent reputation for sticking by their warranties. of those two, I'd choose the car I felt happier driving in, comfort, noise, toys, looks, handling wherever your priorities lie.

At 15k miles a year you could maybe look for an economical petrol and avoid "potential" issues and wear and tear discussions with the warranty people over clogged dpfs, injectors, flywheels that afflict some used diesels. The Avensis 1.8 petrol is a decent motor, good economy and would cost you a chunk less to buy than an equivalent D4D.

If space is very important then maybe look at a (2 year old) Skoda Superb, better interior than the Octavia, more sound proofing, 1.4TSi petrol engine goes well, economy would take a bit of a hit but its a very big, comfy car with a decent dealer network. Somebody will no doubt be along with a shout for a Mondeo which wouldn't be a bad idea.