John wrote:
I have an old (45years) green-yellow conifer on my boundary. It's
higher than the eaves of my house and at its widest point about 4
metres - 2/5ths of this in my neighbours garden.
What's the best way and time to reduce its width and height please?

You don't happen to know what kind it is, do you? Few mature conifers
respond elegantly to pruning, as a quick trip round any suburb will
testify. You could experimentally cut back the branches as long as you
leave healthy green growth on each, and see how it looks. You can then
take out as much of the top as you like, and I'd say autumn was as good
a time as any: but you may find the effect unattractive, even after
it's had a year or two to fill up the space.

My own way of getting the top off may not appeal to a more sensible
person, but it would involve wiggling the ladder in through the
branches till I thought it was securely lodged. The "four up, one out"
rule of ladder work still applies. Then saw until the top starts to
topple without actually coming free. When it's bent down enough not to
fall too hard or in the wrong direction, cut through the last bit. You
have somebody steadying the ladder at the bottom, of course:
traditionally, she will say it's your fault when her hair gets full of
sawdust and stuff, but it's equally traditional to ignore this slander.

It's none of my business, and I haven't seen it, but my intuition is
that you may be better off getting the tree out altogether. Are there
any others obviously of the same variety in the neighbourhood? If so, a
little snooping may give you an idea of what's in store.

--
Mike.