Thank you all.
Emma- I think your advice is good because often I don't get much every 4 hours anyway and my breasts practically don't feel at all full at every feed but everay second feed there is more but still engorgement is never an issue these days for me. After all, the more pumping the more the message is going out to produce more milk.
He had one formula meal yesterday for the first time

I could only pump 100ml for the bedtime feed and he was still hungry. I just don't accept that that is enough for a 4 month old baby anymore.
I will let you know how it goes.
After fighting through a week of mastitis at the beginning and severly cracked nipples I can still say I am proud that we finally 'got it' and I could offer bm for this long. It is amazing how there is so much focus on technique and latch on etc... but hardly and books mention temprement of a baby and that 2 people are involved in the relationship and the emotional dynamics of bf. So many later bf problems involve this relationship and you rarely hear or read about when your baby just does not want it anymore.
I thought our biggest challenge was learning the physical technique of bf but I so had not banked on this!
Just shows you that you have to be flexible and follow LO signs.
Michelle