Mr Mercer said he was "ashamed" of his behaviour and had decided to "fess up" by standing down straight away.
This will trigger a by-election in his Newark constituency in Nottinghamshire.
Mr Mercer was filmed by undercover reporters last year apparently agreeing to set up a parliamentary group to push for Fiji to return to the Commonwealth.
This of course may offer an opportunity to UKIP who are currently soaring in the polls and have now surpassed Labour as the front runners. The BBC continues:
Under parliamentary rules, a by-election cannot be held before that date.
On that we will have to wait and see.
This certainly adds to the growing "election fever" that seems to be everywhere except perhaps amongst the voters. There will be local elections across England in May, plus of course the European elections. It is my intention to cover these events but from a different perspective to that offered in the mainstream media with which I obviously cannot compete.
What interests me and will come as no surprise to regular readers of this blog is the political fringe. There will be various challenges by the far-left in the form of the Trade Union and Socialist Coalition in the local elections, NO2EU and Arthur Scargill's Socialist Labour Party in the European elections. Interestingly the SLP are only standing candidates for the European Parliament in Wales.
The fate of the two fascist MEPs Nick Griffen and Andrew Brons will also be decided in May. They are no longer in the same party having fallen out. Brons has set up the misleadingly named British Democratic Party with a handful of other of boneheads which he is the self appointed Fuhrer.
The Hope Not Hate campaign is up and running against the far right and you can find details: here
There will be others on the fringe and I'll try to fit in the more interesting ones.
Watch this space!
In case any ones wondering I will be voting Labour.