Dave,
First, he is talking about a widower whose wife was murdered by an extremist six months ago

That is not shocking because Brendan instigated the exchange, criticising Farage.

Second, he smeared an organisation that exists to drive back racism
Did he? I think it was legitimate criticism of an organisation hostile to non-fascist, non-racist UKIP, that Farage states has used violence to disrupt harmless UKIP meetings.

at a time when hate crimes have surged after a referendum campaign made inflammatory by politicians including Nigel Farage.

You have been unable to produce anything inflammatory from Farage.
I do not believe he has been at all inflammatory, but am open to being proved wrong.

In case it is unclear the bit in quotes starts the Farage despicable quote.

Here is the whole quote. Please explain what is despicable in it?
"Well, of course, he would know more about extremists than me, Mr Cox, he backs organisations like Hope Not Hate, who masquerade as being lovely and peaceful but actually pursue violent and very undemocratic means."

'is shocking' begins an explanation of why he is loathsome

I have explained above why it does not do that.