Large banks offering an array of financial services are finding it harder to access capital in the wake of tougher regulation, the former head of Barclays told CNBC on Wednesday.

"For many years—really, for 25 years—consolidation, growth and increasing complexity was the trend and universal banking had a capital advantage. And I think today, there is a capital disadvantage in some ways for the universal banking model," Bob Diamond told CNBC in Cape Town from the World Economic Forum.