Just thought I would post this for anyone who like us, until yesterday, has not travelled to the UK via Istanbul.
On the whole the journey was very enjoyable although it increased our travelling time by approximately 2 hours. Providing you book your journey from Dalaman to your UK airport, your luggage is taken from you in Dalaman and transferred to your onward flight at Istanbul. You are also provided with boarding cards for each section of your journey at Dalaman airport which makes your transfer in Istanbul hassle free (no further checking in to go through). We were pleasantly surprised by Dalaman domestic airport, it is bright with plenty seating and a few shops and cafes.
Ataturk Airport is enormous but don't be put off, International Departures are clearly signed from when you enter the airport terminal. It is quite a hike and I would advise anybody with walking difficulties to get wheelchair assistance but for the fit and agile it is no problem. Once in the departures building you just go through security and passport control. When you have cleared passport control you will see Duty Free ahead, and at this point anybody who, like me, needs a nicotine fix, turn right and take the escalator to the next level, turn left and follow the signs to "the terrace" (sounds a lot nicer than it is) where you can have a ciggie. Also the airport is so vast that you have a very long walk to your departure gate.
I read on a previous post that there were lots of nice lounges but didn't, on this visit, have time to find them.
We found Turkish Airlines to be very efficient and the staff extremely pleasant. Good legroom, comfortable seating, breakfast and a hot drink on the first leg of the journey and a very nice lunch of chicken breast, sauted vegetables and mashed potatoes washed down with a nice bottle of wine on the second leg of the journey.
We would certainly do it again and just wish that the winter flights did not result in such a long stopover. Guess it will be Antalya again in the winter unless we can find a connecting flight to Dalaman with Pegasus or Atlas Jet.