So im really busy during the days with work and everything, and would love to play my horn in the evenings, without disturbing/waking the neighbours.

I wondered if silent mutes existed - I'm thinking something that blocks all the sound, so it is virtually impossible to hear. Does this exist and if it does, does anybody have any experience with it??

I saw something to that effect in the local music store where I live. It's called Silent Brass. I've never used it myself nor had any need to because my closest neighbors are 1/4 mile away. It might be a thing worth trying. The next time I go into the music store I'll ask someone there and see what they think about it.

Yamaha makes the Silent Brass system. And Best Brass also makes a silent practice mute. I have used both. I prefer the Yamaha as it is quiter than the Best Brass system; but the Best Brass system is not as bulky.

One problem many people have with them is that they try and play to hear themselves, which is exactly what you are trying to avoid. If you use them properly, they cut the sound way down. When I have to warm up for an early morning performance; or when I have a hard part I need to work out late into the night I use my Yamaha and my wife hasn't complained about it yet.

Ah ok, i've googled them both and am I right in thinking that they block all the sound, but you wear earphones which you can hear yourself through??

They block a lot of the sound. I don't use the electronics to listen, but I also play by feel and not by listening. You can do either.