Lost key to TV cabinet with barrel lock how can you open it any advice gratefully received?

It depends on the latching mechanism of the lock.
Did you ever look at the back part of the lock?

If it's a spring loaded wedge shaped latch, like you have on a door, you can slip a knife in above or below it and slip the latch out of the striker plate.
There'd be a notch in the other door with metal plate with a square hole in it.

If it's got a metal strip that turns with the lock when you turn the key and catches in a hook or butts a metal plate on the other door, you're going to have to drill it out.
It's not very hard to do, all you need is a drill and a 1/4" bit. Drill out the spot where the key goes in. This will drill out the tumblers.
Once you're done you can open the lock with the turn of a screw driver.
The lock is cheap enough and you can pick up a replacement at most hardware stores.

Picking locks is an art, but there's one thing you can try.
If it's a conventional lock, and the key looks like most padlock and tool box keys, stick a hair pin or a very skinny hex key into the lock all the way to the back and then angle it so that the end you're holding is headed down. Some inexpensive locks have a release that will allow you to pull the lock cylinder out and you can then open the latch with a screw driver when you've got it out.

Good luck!