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So-called affinity marketing - where there is a common bond among members - is big business. Members of clubs, societies and political parties are all the target of deals arranged through the parent organisation, as are employees, union members and sports fans.

Affinity deals are often linked to an organisation's activity. For example, the Kennel Club promotes its own dog insurance while airlines have discounted hotel and car hire offers for frequent flyers. Trade unions often provide employment law advice.

Mark Myers is director of partnership relationships at friendly society LV, previously known as Liverpool Victoria. It specialises in affinity ties through its Frizzell subsidiary, which has deals with several unions, the Caravan Club and the Civil Service Motoring Association.

Why are affinity deals so popular? John Bryant is head of flexible benefits at Jardine Lloyd Thompson, which helps employers arrange offers for their workforce. Deals he brokers include discounted mobile phones and bikes.

Likewise, if reports come through of poor service, then a club can demand improvements from the affinity partner or threaten to take their business elsewhere.

Companies also have to be sensitive to the club's membership. For example, it is not possible for a bank or insurer to sign up to offer loans in the name of a club, then reject half the people who apply as being too high a risk. Members will get angry.

If you are a driver with a chequered claims history, this can mean excellent prices for motor cover. But those with a perfect driving record might find a keener deal on the open market.

Like a good marriage, affinity deals work best when partners are well matched. John Price can trace his relationship with the Civil Service Motoring Association back to 1957.

The couple, who live near Wantage in Oxfordshire, also buy insurance for their Swift Challenger caravan through the association, which has been partnered with Frizzell since the 1920s. CSMA customers get 10% off Frizzell's standard insurance rates. John says: 'I have seen insurance-a couple of pounds cheaper, but I am not prepared to risk a move because the service we get through CSMA has been excellent.

Selling through an affinity group can be cheaper for providers than dealing direct with the public. Companies typically get better response rates to advertising and mailshots. This means they can be more generous in what they offer affinity customers.

For some groups, for example classic car clubs, the attraction of affinity insurance may be a claims service that understands their particular requirements. While a typical motor insurance policy will say that the insurer owns the wreck if a car is written off, a policy arranged for an enthusiasts' club may allow the owner to keep the vehicle for spare parts.

Income from affinity deals can be important to clubs and charities. They may earn a commission on each product sold or share a percentage of customers' savings.

A recent affinity deal is a savings account launched last year by Coventry Building Society in support of the Hospital of St Cross in Rugby, Warwickshire. The instant access account pays savers 4.25% gross interest, with a further 1% of the average balance over a year going to the Friends of St Cross charity.

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