deputy pm said he would block a new coalition deal over welfare cuts .
he pledged to force david cameron to impose new taxes on the wealthy .
the liberal democrats have called for £ 3bn of new welfare savings .
coalition has slashed £ 20bn off the benefits bill in five years since 2010 .
mr clegg said tories now ` lashing out ' because they know they are losing .
asked if he was proud of his record in power , he said : ` hell yes '