The county was left for a bill of more than £13 million for the purchase and conversion of Landmark House – more than it had originally planned to pay for two buildings – it emerged today.

The authority’s scrutiny committee is to examine the purchase and conversion of Landmark House on the edge of Ipswich at its meeting next week.

And it will be told that the development will save council taxpayers in Suffolk £1million a year – up from the £500,000 originally planned.

The county shares Landmark House with the police. Originally the two authorities had planned to buy both that and St Edmund House in Rope Walk.

In 2010 the cost of that scheme was estimated at £25.55 million with the county paying £13.15m.

However the following year it was decided not to buy St Edmund House and concentrate Landmark House which would have to have extra development.

The total cost now comes to £23.827m, of which the county’s share is £13.158m.

The report reveals that the authorities paid £3.6m for Landmark House, which was originally built for high-tech company Agilent 10 years ago and pulled out of the town before occupying the building.

The original guide price for Landmark House was £12m, and the reduced price reflected the fact it had been unable to find a buyer and needed millions spent on its conversion. There are now 850 people based at Landmark House – 400 Suffolk Constabulary employees and 450 county council staff.

The report prepared for the committee says that the cost of buying and converting Landmark House just over half what it would have cost to built a new building to the same specification.