The ringleader of the London Bridge terror attack was filmed telling a former Muslim he should 'be killed' for leaving the religion less than a year before the bloody massacre.

Khuram Butt was wearing a Superman hoodie and smiled as he threatened another man in Hyde Park corner, the BBC reports.

The altercation is believed to have happened in August last year, nine months before eight people were murdered in the Saturday night attack on London Bridge.

The man who filmed Butt has now said he wishes he had gone to police with the footage.  The witness, from north west London, told the BBC: 'He came up and said "I want top have a discussion". 

'He turned suddenly and got personal and started threatening that I'm going to kill you.

'He was just threatening and very aggressive. I was scared, he said "if you do not honour my religion you should be killed".                                                        

• Khuram Butt was wearing Superman hoodie as he argued with people in London
• London Bridge terror attack ringleader told former Muslim he should 'be killed'
• The altercation is believed to have happened in August last year 
• Man who filmed Butt said he wishes he had gone to police with the footage