Frame no. on a Carlton Cobra ?

[Nolycrahere]

Hello .. where do I find the frame no. on a Carlton Cobra ? I've looked on the crank casing and no sign of any lettering, although someone had welded it before I bought it (1988 - £10). Been riding to work daily since then but now want to register it & ideally need the frame no. Rather muddy currently but lettering is not obvious elsewhere. Many thanks !

 

[Spokesmann]

Left hand side rear drop out usually.

 

[Nolycrahere]

Left hand side rear drop out usually.

Many thanks for coming back to me .. after some cleaning I found it on the back of the saddle post.