What is the spec of the ariel plug on the ariel originally fitted to the '99 Blazers please? I have had my ariel broken street side by a moron while parked up. The ariel cable has a very small plug (by European standards anyway) that has a
3/32" pin on it, the replacement ariels here are DIN or ISO and have a 1/8" pin and larger barrel of nearer to 3/8"?
My alternative is to have a complete new ariel and audio but the radio I have works perfectly well

 

You will need to get an adapter for what you want. There are other ways to do it, but you may get poor signal quality if you don't have the proper shielding on the wires. The adapters here in Canada run about $5, so roughly 2£ for you. Just look for a GM to ISO adapter. Alternatively, since you are across the pond, you might have a better chance finding an early VW antenna adapter which uses the same dimensions as GM does. Just make sure if you go that route, get a VW adapter that fits cars before 97. Post 97 have amplified antennas, and you wouldn't get anything from it.

You will see a price difference between the two, so it takes the guesswork out.

 

Thanks for that, I have ordered this one:
Metra 40GM21 Antenna Adapter with Mini Barbless Connector for 1988 2006 GM | eBay