Going to True Blue's question,yes the Queen can summon the Prime Minister and inform him or her that she is dissolving parliament and orders the Prime Minister to call an election. I blieve she can do so without reason,but to prevent a clash,I think it would be wise if there was a solid reason to carry out this act.
I once read that the Queen threatened to do this if Blair had signed up to the EU constitution without consulting the electorate. However,saying that,as it is never minuted what is said between ER & PM,it would be purely speculation,but somehow,the Queen's threat to him would have been plausible.
Ta Ta
Marky B