By Benedict Tetzlaff-Deas A Tory MP was left struggling for words on BBC Question Time last night after Fiona Bruce asked him about the increase in tax burden following the budget. The awkward exchange in Cardiff came after guest panellist Welsh secretary David TC Davies claimed that the 2p cut in National Insurance announced this week would “make a difference” to households across the UK. On Thursday night’s edition of the long-running question-and-answer show, Fiona Bruce picked out this comment and asked: “When you say everyone who pays National Insurance will be better off, according to th…