The Conservatives are on course to spend £1 million on Facebook ads before the election

The BBC published an invoice sent from Facebook to the Conservative Party referring to September last year which amounted to £122,814 in total. Of this, about £13,000 was spent buying likes for the Conservative Facebook page, and £11,800 on likes for specific posts.

Another invoice, obtained by the watchdog website Political Scrapbook, refers to November last year and shows a bill of just £3,000 spent on Facebook in the Rochester and Strood by-election.

That election was won by UKIP. The low level of Tory spending on the campaign suggests party officials were not interested in wasting money on a race they believed they would lose.

The Tories also spent £4,000 on video advertising. Video ads are one of Facebook's newer products.

At this pace, the Tories could spend more than £1 million on Facebook ahead of the general elections in May.

On both the invoices provided, the biggest bill was for email collection (£96,617 in September and £71,147 in November). Conservative supporters are encouraged to hand over their email addresses so the party can use them to plead for donations: despite the rise of social media advertising, email is still the main online channel for political campaigns in Britain.

The Conservative Party declined to comment on this particular issue when Business Insider reached out.