Well I did DFW-LHR-DEL in Sep and no questions were asked , granted I had the emergency visa even though I also had an OCI "U" visa. I got the emergency visa as I misplaced my actual OCI booklet.
Please note that this was in Sep and GOI keeps adjusting/making rules as it goes. However, BA did decline boarding to 2 US permanent residents with Indian passport and one with H1B visa on my day of departure from Del.
India UK bubble does allow transit of foreign nationals or their spouses via UK.