Belgrade connection to London bombings?

The Sunday Herald has what may (or indeed may not) prove be a very significant story about the London bombings:

One other theory is that the terrorists may have got their explosives from Belgrade, the Serbian capital. According to Israeli security analysts, British anti-terror specialists have flown to Belgrade with samples of the explosives used. A number of illegal weapons traffickers operate out of Serbia and are known to have connections to terror groups and repressive regimes around the world. Americans have traced weapons seized in Iraq to Serbia. (Sunday Herald)

I assume this is based on the story which appeared on Saturday morning on Debkafile, an Israeli website of questionable trustworthiness.

Belgrade is where al Qaeda goes shopping for the explosives and arms for its terror attacks, according DEBKAfile’s exclusive intelligence and counter-terror sources. Thursday, July 7, eight hours after four coordinated blasts hit London transport and killed at least 50 people, British terror experts were on a special flight from London to the Serbian capital. (Debka.com)

In its favour, the story appears to have come out before the Metropolitan Police press conference that confirmed high explosives were involved.