You can't and why would you want to? By the way Guest we are all real live human beings on this site so when you ask a question just remember that and use the please and thank you words.

since when have we needed to be SO rude to guests!!!!
I am ashamed to be part of this.
also it is nobody else,s business if someone wishes to cut something in their own garden down surely!!!!!!

Helen, Guest specifically states that they do not want to cut down the tree only to kill it, that isn't possible.

I think you'll find the law in the UK will disagree with you Helen, with regard to cutting down trees in your own garden. You can't prune/fell/kill a mature sycamore (even if its yours!) without asking your local council for permission first. If you do you can be prosecuted, fined and be made to plant a replacement which you may have to look after for up to twenty years.
The fine could be twice the value of the timber...very costly!
Plus a criminal record too!
ps. I don't think moon grower was being rude. We are real people not a computer generated facsimile. Being polite when asking generates a polite response when answering.

Thank you Stjohntongue

you're very welcome, Moongrower.