The British Library has apologised to users for the disruption to services resulting from this week's strike.
Members of the Public and Commercial Services union downed tools on Monday over pay bargaining, and further action took place on Tuesday and Wednesday.
The library was determined to carry on business as usual, prioritising its most vital services. A statement said: "A reduction in staff numbers may make delays in services or the closure of some reading rooms unavoidable. The library will try to maintain services to the public at St Pancras, including the bookshop, the exhibition galleries, the restaurant and cafe."