Can I cut back a hugely overgrown lilac now?

[Chameleon2003]

As the title says - causing the neighbours a few problems so would like to do it now rather than wait until after it flowers in the spring.
It's years and years old so would hate to kill it.

It’s unlikely that you would kill it, but you probably won’t get any flowers.
We inherited a lilac growing in a hedge, every year the previous owners cut it with the hedge. We started to avoid cutting it and it flowers beautifully.

I agree with Beebumble2 cutting back now shouldn't kill the lilac but it will affect flowering next Spring.
I had to do this a few years back and it was only an issue the following spring.

Thanks - will go for it I think.

If you're doing major cutting back of anything, it's best to spread it over 2, 3 or 4 years. Can you cut back the branches that are causing your neighbours big problems this year, leave it looking lop sided, then complete the job next year?