9. A speech recognition system comprising: a processing module programmed to: obtain a speech sample utilised to authenticate a user as part of an authentication process; process the speech sample to train one or more generic acoustic models for speech units associated with the speech sample and to subsequently store the trained acoustic model(s) in a personalised acoustic model set; selectively re-train the acoustic model(s) based on additional speech samples provided by the user containing corresponding units of speech; responsive to determining that the user has accessed a speech recognition function, the processing module is further arranged to access the personalised acoustic model set for recognising subsequent user utterances; and the processing module being further programmed to determine a measure of quality for each of the stored acoustic models and continuing to regenerate the acoustic models until the quality measure reaches a predefined threshold.
9. A speech recognition system comprising: a processing module programmed to: obtain a speech sample utilised to authenticate a user as part of an authentication process; process the speech sample to train one or more generic acoustic models for speech units associated with the speech sample and to subsequently store the trained acoustic model(s) in a personalised acoustic model set; selectively re-train the acoustic model(s) based on additional speech samples provided by the user containing corresponding units of speech; responsive to determining that the user has accessed a speech recognition function, the processing module is further arranged to access the personalised acoustic model set for recognising subsequent user utterances; and the processing module being further programmed to determine a measure of quality for each of the stored acoustic models and continuing to regenerate the acoustic models until the quality measure reaches a predefined threshold. 12. A system in accordance with claim 9 , wherein the additional speech samples are provided by the user either during enrolment with the authentication system or as part of a subsequent authentication session.