Ministers speaking in support of equal marriage claimed today that it could give the British economy a boost of as much as £18 million per year.

The government estimated that more gay couples would want marriages than civil partnerships, meaning that an estimated 3,000 marriages will take place on top of the 6,000 who already get civil partnerships every year.

The spending on these could amount to an extra £14.4 million per year going into the economy, based on an average £4,750 per wedding.

On top of this, couples who previously had civil partnerships will be able to convert to marriage. The related ceremonies have been “conservatively” estimated at £3 million spending.

Due to the difficulty of correctly identifying specific financial benefits from equal marriage, the government impact assessment put the benefits at between £100,000 and £18.6 million

There may also be an influx of couples from countries which don’t allow equal marriage coming to the UK and getting married during their stay, contributing to the economy as tourists as well as through wedding costs.

Speaking to the Evening Standard, Mayor of London Boris Johnson said: “Marriage should be open to all, regardless of sexuality… I have no doubt marriage equality is of benefit to our economy, and that in itself is a good thing.”

The Lesbian and gay Lawyers Association said: “The requirements for residents are relatively easy to meet (contrary for example to Spain), most people speak English and England is known for picturesque country settings. We expect a modest boost to the tourism industry.”

At the weekend, the Government said that the costs of introducing same-sex marriage in England and Wales would cost between £3.3m and £4.7m, mainly to do with IT costs of logistically implementing the change.

Out4Marriage said: “Even if it costs £4.7m to introduce the IT and other changes needed, it seems like a small price to pay for England and Wales becoming a more equal society.”

After the bill was introduced in the House of Commons by Culture Secretary Maria Miller on Thursday, the bill was published by the Government on Friday. 

The bill has divided Conservatives, with former Defence Secretary Liam Fox recently describing it as “ill thought through and constitutionally wrong”.

More than 100 Tory MPs are thought to be against the idea.

However, the bill is likely to secure a majority in the Commons with the support of Labour and Liberal Democrat members.