Battles over wills are some of the most bitterly fought of courtroom contests - and they are on the rise. The number of High Court cases involving wills and inheritance rose by 175 per cent - from 83 in 2006 to 228 in 2007, according to the latest figures.

Broken down, the figures show an increase in wills disputes of 153 per cent, from 73 in 2006 to 185 in 2007; and in inheritance disputes of 330 per cent, from 10 in 2006 to 43 in 2007.

The figures have been highlighted by Wedlake Bell, the City law firm, which says that the actual number of disputes will be far higher than this as only a fraction of cases end up in the courts, with most settled out of court.

So what is the reason? Wedlake Bell puts it down to a mix of factors: the increasing complexity of family structures, the soaring value of estates, people's longevity and more charitable giving.

Fay Copeland, a solicitor with the firm, said: "We are seeing more and more cases where disputes arise from spouses of first, second or third marriages. Things get even more complicated when it comes to provisions for the children of each marriage. People can end up very displeased with the size of the slice of the estate they receive and have fewer qualms about taking matters to court if they feel they have been treated unfairly under the will."

Long-term cohabitation can also bring problems, she adds. The family of a deceased person may object to provisions made in the will for a cohabitating partner if the couple never maried; or a cohabitating partner might contest a will that does not include provisions for him or her.

Then there are illegitimate or stepchildren. If a man helps to raise such as child with regular maintenance payments, there could be grounds for contesting a will that does not provide for the child after his death.

Wills are not set in stone, Copeland adds. They can be challenged - if, for instance, there is a need for continuing maintenance payments.

Another increasingly common reason for challenging a will is mental incapacity. People left out may think the deceased was no longer of sound mind when the will was drafted or vulnerable to pressure to favour one beneficiary over another.

Finally, there is the growth in charitable giving. Copeland says that many older people don't feel as connected to their children, with families dispersed across the UK and worldwide. Her firm has seen an increase in people leaving sizeable estates to charitable institutions "as they feel closer to these than to their children".

She adds: "These can range from the legendary cat shelter through to medical research charities." Disgruntled children then challenge the will. The best way to protect against such a dispute, she advises, is to leave a letter with the will explaining what is intended and why. That can help if the will is disputed.

All this should not put people off making a will. Carl Marston, of SAS Daniels LLP, Cheshire's biggest law firm, says that single people, for instance, are among those most likely not to bother with a will.

One in five of single people do not make one, which means that their last wishes remain unheard or their estate is left to the intestacy rules, he says. "This puts at risk any potential inheritance-tax savings and leaves people's affairs, in most cases, more difficult to unravel and administer in the event of their death."

As a result, charitable wishes will be unfulfilled, members of the family may not receive anything and those whom the deceased wanted to benefit may not do so. "Of course, in the event of no family, the whole estate may end up going to the Crown."

Another downside is that the creation of trusts and powers of attorney may also be overlooked as planning options and any funeral wishes not specified, he says.

From this month, though, new intestacy rules take effect, which ensures that spouses and civil partners will receive more than they did, when a partner dies without leaving a will.

Sarah Albury, senior associate in Mishcon de Reya's private client group, said that the changes were welcome because there had been no increase since 1993 and current market conditions aside, the increases would bring the legacies into line with the increase in property prices and the overall rise in the value of an average estate.

So from February 1, the new statutory legacy payable to a surviving spouse or civil partner increases to £250,000 (where there are children) and £450,000 (where there are none).

However, Albury cautions that people should not be misled into thinking that they don't need to bother with a will - the "only way to ensure that those you love and are obliged to care for are adequately provided for". Leaving it to chance, she adds, can bring "heartache, increased taxes and significant costs for those left behind". In the long run, that benefits only the lawyers, or the taxman.

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