Thank you for this comment Willow tree
Last year I had a in-depth conversation with the head of a US southern state's gang crime unit, a Detective ***** regarding this very issue (i am doing a documentary on latino gang crime in the US). I asked him whether there is a link between AQ and MS13. He categorically stated that there is no link. The only link was the head of MS13 converted to Islam and left the gang, a death sentence has been placed on his head for deserting the gang. The FBI picked up the news of his conversion, notified the media and the snowball effect happened.
MS13 does not work with rival drugs gangs. They do bad things for money, people smuggling, weapons etc but MS13 are not involved in AQ, this is a myth.
As for regimes in South America, yes this is true but only on a socialist level, an alliance between states and governments against the US, ie, Iran/Cuba/Venezuela vs the USA.
This is not to say that some latino gangs don't "work" with AQ but it's unlikely. People smuggling for a price? Yes. Supplying weapons for a price? Yes. Nuclear weapons? Hell no! Latinos in the US are in their millions, they would never allow a foreign terrorist group to smuggle in nukes to kill their own people and ruin their drugs empire.
The gangs in the UK are for the most part involved in the Jihad against the West, Ms13, Latin Kings are not against the West per se, they are against Authority but remember that the USA is their home.
The Pakistani gangs are at war with the UK, the British and their government, they do not consider themselves to be British and feel that muslim deaths in a muslim jihad operation will martyr their muslim victims. They would welcome a nuke attack against London.
Heroin is not the biggest source of income for MS13, Cocaine, meth, guns and prostitution is their main income, I just dont see that to make a few million they would smuggle in a bomb that would kill millions and hamper their business, which would result in the loss of billions of $$ over the following years and the arrest of their entire leadership. Imagine the backlash if MS13 was found to be the ones who imported the bomb/s! They would be wiped out by the US government and armed citizens. MS13 have it too good at the moment, open borders, a crack cocaine epidemic and a massive illegal latino population for them to feed off of. A nuke would wipe out their profits and end their empire overnight.
Lastly, if a nuke was to be smuggled in it would come via the sea ports, these areas are seriously under-searched and underfunded.