Johnson, while on the way to Hampshire to lend his support to Tory candidate Maria Hutchings, accused his party's coalition partners – and the Lib Dem leader Nick Clegg in particular – of indecision. He also insisted it was the Conservatives' "constitutional duty" to kick the Lib Dems in a very sensitive place.
The London mayor brought traffic to a standstill as he arrived in the constituency and immediately began meeting and greeting electors with Hutchings.
But even before he arrived, comments made on the train about the deputy prime minister and the Lib Dems were all over Twitter.
The Daily Record's Westminster editor, Torcuil Crichton, quoted Johnson as saying: "It is our constitutional duty to kick the Lib Dems in the … well, do they have any?" And: "Lib Dems are wobbling jellies of indecision and vacillation, particularly Clegg." Crichton also had Johnson saying of Clegg: "His single contribution to politics has been to do a U-turn on tuition fees and make a song about it. That's all he's done."
It was shaping up to be a lively day in Eastleigh. The Labour candidate, the author and satirist John O'Farrell, was trying to get the message across that this was a "two-horse race" – between Labour and the Conservatives/Liberal Democrats.
Labour was dressing up two activists as jockeys to illustrate their point. "And one of the horses is carrying both colours, yellow and blue," said O'Farrell. "This byelection is a choice between the coalition and Labour."
Ukip, however, claim they are very much in the running. They revealed that two former Liberal Democrat councillors, one an ex-mayor of Eastleigh, are backing their byelection campaign. Glynn Davies-Dear, a former mayor and a well-known figure in the Hampshire town, and ex-councillor Andrew Moore are both supporting Ukip candidate Diane James.
Davies-Dear, who used to work in the office of former Eastleigh Lib Dem MP David Chidgey, said he had become disillusioned at the direction the party had taken, locally and nationally.
The Lib Dems dominate Eastleigh borough council. Davies-Dear, who said he had been on the left of the party, claimed: "When you have nobody to fight, you begin to fight each other. You're fighting for money and power, that's all you care about."
Davies-Dear said he had also been "disgusted" by the actions of Chris Huhne, whose resignation has led to the byelection.
He said he had been worried by Ukip's rightwing views on immigration but, having spoken to James, had decided the party was not "racist". He said: "I think she would be the best MP for Eastleigh, simple as that."
The Lib Dems dismissed the "defections", saying that both had not been deemed strong enough to continue to represent the party and so had left in 2011.
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