The basinette is a god send except if there is turbulance and then you have to carry them but at that age he shouldn't wake up! You'll also have a load of space in front of you to store the bags which makes it easier...about two and a half feet I think which is great

The only bad thing about the front row is the arms don't come up to make the seats into one but at least you'll have leg room.

You'll be fine The last time I went back to the UK I flew on my own with an 18 month old, a 5 year old and 7 year old...thought I would suffer from PTSD it was that horrific! But you and a 4 month old will be easy.

Also I would request assistance at Heathrow - that way they will take you through customs, grab and push your bags for you. It's hard to do this on your own with a pram...trust me lol!