The Preference Service, which is majority-owned by the UK and Dutch Post Offices, has a database of 4m households and 350,000 email records.
IPT has a database of 5m email records of which 2.1m have postal addresses. It operates a range of websites which collect consumer data via questionnaires.
IPT will now place more emphasis on its postal division, which will be headed by The Preference Service's managing director Thomas Adalbert. All of The Preference Service's staff of around 30 are moving to IPT's central London offices.
Martin Kiersnowski, chief operations officer of IPT, said: "Both The Preference Service and IPT have built successful data businesses based on the principle of permission. Our combined data resources will give us the largest volume of recently acquired opt-in data in the UK."
In addition, IPT has raised £3m through a share issue to replace the cash it is using to buy The Preference Service. It has been publicly quoted since December 2004, when it raised £4.5m by floating on the Alternative Investment Market in London.
IPT also provides email delivery and market research and has a list of blue-chip clients including Lloyds TSB, the AA, British Gas and Tesco. It made a profit of £1m on 2004 turnover of £8.4m.
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