I think you will have seen an ex-BR Class 90 on an LNER service.
DB Cargo have a fleet of 90s normally used on their freight trains, but they hire them out to other TOCs as well.
LNER need extra locos because of a shortage of Class 91s.
They are indeed DB locos, but they don't have German provenance.
So far, no foreign-based locos have ventured onto UK tracks, if we discount Eurotunnel and some emergency workings on HS1.
They would be out of gauge on our smaller profile network, and would not be equipped with Network Rail safety protection (AWS/TPWS) and other UK standard kit.
To further confuse, 3 class 90s were painted up in 1992 by BR into then DB, SNCB and SNCF livery as part of a joint promotion.
DB bought the EWS business from Canadian National in 2007 and slowly repainted the class 90s into DB Schenker livery.
A later reorganisation renamed the TOC as DB Cargo.