Republican presidential hopeful Donald Trump has more than doubled his monthly campaign spending to $18.5m (£14.1m). But the property mogul's expenses still lag far behind that of his Democrat rival Hillary Clinton.

Despite his reputation for brash opulence, the billionaire's campaign spending is far less than the campaigns of both Barak Obama and Mitt Romney in 2012, according to the BBC.

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Hillary Clinton's campaign spent more than $38m in July, a Federal Election Commission report released on Saturday (21 August) showed.

Throughout his campaign for the GOP nomination and beyond, Trump has touted his own wealth as one of his great strengths in campaigning.

In the past, he has said that his wealth means that he cannot be corrupted by money from donors, but that Hillary Clinton – to whom he himself has given political donations in the past – could be influenced.

As controversy grows over the level of the former reality star's personal wealth and tax outgoings, a New York Times investigation has shown that Trump's firms are at least $650m in debt.

Trump has had to backtrack on his promise not to take donations and to self-fund his campaign, but the latest figures show the firebrand is running a frugal campaign, in has spent on hats ($420,000) than on TV ads, which began being shown this month.

Millions more went to air travel. The campaign paid about $2m for private jets, other than Trump's own TAG Air, which also collected $500,000.

Clinton employs about 10 times more staff than Trump. She has around 700 individuals on the payroll, while Trump has just 70.

As both Clinton and Trump build up their war chests in the run-up to the election, the Republican candidate is similarly seen to be lagging behind. The Trump campaign brought in $37m for the month, compared to the $52m raised by Clinton.

The largest contributor to the increase in Trump outgoings in July was an $18.5m spend on Giles-Parscale, a web design and marketing firm new to US politics, the AP reported.

The payments show that Trump, who has galvanised a section of the American public, will be looking to draw large funds from a grassroots online campaign.

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