Microsoft owner, Bill Gates, and his wife Melinda, have personally given $500,000 (£313,000) towards efforts to legalise equal marriage in the state of Washington, pushing the total raised by equal rights advocates to $10.8 million (£6.7 million).

The money will go towards Referendum 74, which hopes to legalise same-sex marriage in the state. Washington United For Marriage announced that it had raised the total amount, on Tuesday morning, SeattlePI reported.

Washington United for Marriage chiefs are thrilled by gifts of this size.

Speaking of an earlier gift, Lacey All, chair of Washington United for Marriage, said: “This is just such an incredible gift and comes at a time when we’re seeing significant national money flow to our opponents.”

According to reports, the Gates’ had already donated $100,000 (£62,700) to equal marriage charities.

This is not the first high-profile personal gift equal rights advocates have received this week. Yesterday, The Mayor of New York City, Michael Bloomberg also offered $500,000 (£313,000) from his personal fortune, towards the push for marriage equality in Maine, Minnesota and Washington.

Mr Bloomberg had previously donated $250,000 (£155,430) to the campaign that is fighting to keep equal marriage in the US state of Maryland.

Last week, a large number of Washington-based companies, including Microsoft, confirmed their support for Referendum 74 by signing up to a newspaper advert.

Support for equal marriage in Washington has come from unexpected places, as earlier in October, 63 ex-Catholic priests publicly declared their support for R-74.

On 6 November, Washington, Maine and Maryland voters will decide whether or not to legalise equal marriage in those states.  At the same time, Minnesota voters will choose whether to make a constitutional amendment which would define marriage as only between one man and one woman.