Architect SMC Group has made its biggest acquisition with the purchase of architecture and design company Charter Consultant Architects.

SMC bought Charter for an initial £3.56m, plus two further payments, dependent on Charter's financial performance over the next 18 months.

SMC has been aggressively buying architecture and design firms over the past year - the acquisition of Charter is the seventh transaction since it was floated on the alternative investment market in June last year. In March this year SMC purchased Will Alsop's design practice for £1.8m.

Stewart McColl, SMC chief executive, has been buying firms with strong trading histories so that he will be in a position to compete for bigger contracts. In the year to 30 April 2005 (the most recent audited accounts), Charter made a £1.3m pre-tax profit on a £7.2m turnover.

McColl said: "We are delighted with the acquisition of Charter, a business that was introduced to us by one of our operating companies, which held it in high esteem."

Charter is a design-led architectural and interior design company operating from offices in London, Bedford, Bournemouth and Ipswich. Its clients include BT, Gillette and Trinity College Cambridge. Chris Littlemore, Charter's chief executive, said the relationship with SMC would enhance its commercial position.

SMC and Aukett Fitzroy Robinson are the only two quoted architects in the UK.