I'm not sure where East Anglia is, but I'm thinking you are in the UK. Here in many areas of the US there have been many trees keeping their leaves longer this year. Environmental conditions will cause this.
Hi
I have almost 60 years experience and you are correct - the deciduous plants over here are all going into dormancy later this year than ever before. Don't know if it is global warming or a climate cycle, but it it is a pain as Ashridge Trees lifts nearly 1 million bare-rooted hedge plants (beech, hornbeam, wild rose, hazel, field maple as well as yew, box etc) and we have orders piling up and impatient customers waiting.
And the lateness is a trend over the last ten years it has been later every year without a break.