If you want to know how worried they are about the threat from UKIP then you just need to look at their leaflets and the behaviour of their candidates.
All over the country UKIP candidates are reporting LibLabCon leaflets directly targeting UKIP, warning that a vote for UKIP will split the vote and let in another party. None of them have positive reasons for voting for a LibLabCon party, they just warn about splitting their vote as if they somehow have an automatic right to a certain percentage of the vote. As most people have finally come to realise from recent council by-elections, a vote for UKIP lets UKIP win.
There is also a "false flag" campaign with activists from other parties creating fake profiles on Facebook pretending to be UKIP members and saying ridiculous things to try and discredit the party and antagonise UKIP supporters. One Conservative Party activist happily admitted to doing it when he was caught out and said he was "just doing [his] job". His fake profiles and his own account have since been suspended by Facebook. There are also reports of some of these activists phoning in to radio talk shows pretending to be UKIP members and doing the same thing.
We're currently at DEFCON 2 on the Gandhi scale: