Help with identifying this 26" steel frame

[grk]

The seat tube wall thickness measures around 1.5 mm. Were there tubes made with such thickness? Sorry if it’s a stupid question, but I’m a bit of a noob.

 

[grk]

 

[sam_white]

Shocked that I never noted the frame number or replied to this thread. Sister frame M5090091 is here: https://www.retrobike.co.uk/threads/what-is-it-stainless-steel-frame.80776/
My best guess would be a UK Merlin. No other positive IDs, but the frame numbers are in the same series as two Rock Lobster 853 frames I have listed.
Frame number is September 1995.