Thank you!
The short answer to your question is Leicester Market....  I think they may be from the Far East, as I recognised some of the other fruit for sale as Eastern.  Actually, yes - just wiki'd it - official name 
Pitaya:
	Quote:
	
	
		| also cultivated in Southeast Asian countries such as Vietnam and Malaysia. They are also found in Taiwan, Okinawa, Israel, and southern China. |