Labour frontbencher Chuka Umunna got involved in a spat on live TV after an interviewer asked him to comment on a letter he had not read.

Sky News anchorman Dermot Murnaghan repeatedly pressed Mr Umunna about the letter sent to leaders of English mosques by Communities Secretary Eric Pickles - and even offered to give him half an hour to read it before coming back on screen.

The shadow business secretary - who said he had been invited on to talk about David Cameron's earlier speech on the economy - eventually walked off while the cameras were still rolling, waving his hand at the screen in apparent exasperation.

The bulk of Mr Umunna's interview, conducted via video link, revolved around the economy and employment.

But as it drew to a close, Murnaghan asked him whether he thought Mr Pickles was "patronising" the Muslim community by urging imams to "lay out more clearly than ever before" that British Muslims can be proud both of their faith and their country.

When Mr Umunna replied: "I have to confess, I haven't read the letter myself", Murnaghan responded: "Well, what are you doing in politics? Come on, everyone's talking about it. It's the middle of the afternoon and you still haven't read this?"

The shadow business secretary replied: "With the greatest of respect, Dermot, I wasn't told you were going to ask me about this, but since you've asked me the question, let me answer it."

He said that that extremism was "something for the Muslim community to tackle, but also for all of us it's something we have to tackle more widely".

Murnaghan read out an excerpt from the letter, and asked whether it was "patronising", to which the shadow business secretary responded: "I'm not sure I would use the word 'patronising' for the simple reason that I haven't read the letter. You and I can have this debate if you want, but the wider and bigger issue for us is how we ensure that young Muslim people..."

The interviewer interjected: "Do you want to come on in half an hour's time? It doesn't take long to read the letter and then we can have this discussion."

Mr Umunna replied: "Dermot, I think you are being a bit ridiculous right now and your viewers can form their own views. I was asked to come on and speak about David Cameron's speech on the economy and what was happening around the labour market. Nobody told me I was going to come onto this programme and be asked to agree whether I thought the Government was patronising Muslim people and Muslim leaders.

"I'm not just going to speak off-piste without having actually read a letter. I don't think you're being terribly fair. Your viewers can make your own decision."

Murnaghan responded: "So you're not going to speak until you get the party line right? OK, well we'll have to end it there," prompting Mr Umunna to get up from his seat and leave while the camera was still rolling.