The Home Office has announced a marginal cut in its estimate of the cost of the government's controversial biometric passport and ID card programme.

A six-monthly cost update to the rolling 10-year forecast which soared to £5.7bn six months ago from an original £3.1bn, has now fallen back slightly to £5.6bn in 2007-08 prices.

The official explanation is that there has been a reduction in forecast future passport volumes "due to customers delaying passport renewals" resulting in savings of £85m and a reduction in assumed production and delivery costs of £100m.

But the cost reductions are partly offset by inflation as the 10-year period being forecast moved forward from April 2017 to October 2017.

The reduction was announced as Identity and Passport Service chief executive James Hall revealed the agency is reviewing the use of local post offices and possibly travel agents, currently partners in handling passport applications, in the process in a bid to keep costs down.

The extent of possible involvement has not yet been decided, but the Post Office is looking at developing the ability to record data electronically at branch offices, which might include taking fingerprints from applicants.

The cost estimates involve the service to British and Irish citizens resident in the UK and to foreign nationals, including asylum seekers and immigrants.

The Home Office said the revisions "reflect greater understanding of the work required and current experience of the Identity and Passport Service.”

Current estimates reflect the outcome of a number of competitive tendering processes, the first of which has only just commenced, with Accenture, BAE Systems, CSC, EDS, Fujutsu, IBM, Steria and Thales in the running to become one of five preferred bidders.

They also reflect key assumptions about the number of applications for pas sports and/or identity cards, the operation of the enrolment process and achievable staff productivity, all of which may well change, said the Home Office.

A further breakdown puts ID card-specific costs at £1,005m and those common to ID cards and biometric passports at £2,964m.