Filters fitted to earlier British-built Ruston 2YWM are unfortunately not the same as those fitted to India-built engines. As a result I searched around and found a very helpful supplier, Rico who are based in Daventry. I have now sourced and fitted a suitable replacement element. The Baldwin P15 (601P) fits well in the housing and appears to be working effectively.
Oil Filter for Ruston (India) and Greaves Cotton 2YWM Engines