Below is the reason given by the Home Office for fingerprinting Asylum seekers
The purpose of fingerprinting asylum claimants is to positively identify them and also to identify and deter multiple asylum claims at national and international level. Fingerprinting is also targeted at deterring asylum shopping’ within Europe by recording fingerprints on, and checking fingerprints against, the Eurodac tabase. The Eurodac system is a Europe wide fingerprint database which was established by community regulation supporting the Dublin II Regulation and therefore forms part of European Community Asylum law. The fingerprints of all applicants from the age of fourteen are recorded on, and checked against, the Eurodac database.
The full home office document in relation to this is available here – fingerprinting-asylum