Does anybody know about Plague bodies found during the building of the British Library at St. Pancras c/90's ?

The people most likely to know are the Greater London Sites and Monuments Record. They are the database for archaeology in Greater London and record details of sites, finds and excavations.

Their contact details are at http://www.heritagegateway.org.uk/gateway/chr/herd... . Ignore the link to their online database. The search engine on the ADS site that host the database is not easy to use, I haven't found any records with actual descriptions (just names, grid reference and ID number) and it appears to be a version of the database from 1992. Contact them directly as they are constantly putting new information on their database (I should know I volunteered there back in 2002 when they were inputting everything onto a new database). You never know you might hit lucky and there is a archaeological report of the excavation available for you to see.

It is quite common - especially at sites just outside the historic centre. The bodies are normally re-buried once it has been established they are not recent. (Not only humans - I know a site in Islington which had to be halted as a horses' graveyard was discovered with the attendant risk of anthrax).