Thanks so much for all your replies girls! I was having a serious bad day here and it all just got on top of me.

So tonight I took a little bit of everyone's advice - cut off time for any "Mum I'm hungry" chants was 4pm so no random snacking, but then I gave him a bowl of carrot sticks at about 5pm and had all the kids bathed and dressed, and the girls settled in their rockers by 6.15pm so we could sit down for tea together. We all sat at the table with him on his booster chair again. He had about 40 minutes to eat in the end and he ate everything. At the 25 minute mark, we gave him a 5 minute warning to finish and he had a couple of mouthfuls to go. When DH told him that time was up, he said "But I want a treat!" (icecream and fruit like I eating, having finished my dinner and got bored sitting there) and he finished off the last bit fairly quickly (for him anyway).

I think we lost our way with meal times when the twins came along, and I didn't know how to get it back so thankyou so much for your advice! I blame myself partly for his slowwwwww ways as I loving sat and spoon fed him for far too long. So not doing that with the twins - just ordered the book on Baby lead solids lol.