I know this thread is an oldie but there's no statute of limitations on cold cases, is there? No thread left behind!

Don't know if [MENTION=312221]jo1010[/MENTION] still comes by, or even owns this bike anymore, so I'm updating this for reference.

The frame here was made by Rick Powell of Dinnington (South Yorkshire). Rick worked at Carlton for decades, becoming chief frame paint sprayer and eventually shop foreman. After the Carlton shop closed in 1981, he started building under his own name. The company was called "DD Enterprises" which explains the "DD" in the serial number. I vaguely remember reading somewhere that DD Enterprises was an existing (possibly family) business that frame building was merged with.
Also, I've only ever seen "DD" decals on the head tube of all Rick's frames, which would explain the lack of head badge rivet holes.

With the serial of DD136, it would be one of the earlier examples, so probably early to mid 80s (as [MENTION=101154]big chainring[/MENTION] pointed out). The green example below has a number in the 800s. Rick built until 2003, but I've not come across any records of numbers from that period.

Examples: