Not as such. The Queen presents herself to open parliament and is the head of state and of the commonwealth. She does however still retain the power to dissolve parliament in theory but it is uncertain what would happen if she tried.

Only the Queen, as head of state, has any formal authority. It is important to distinguish between the powers of the Crown (which are considerable) to those of the Queen, who, as an individual, has not much power but a considerable degree of influence. She has regular meetings with the Prime Minister who briefs her on what "her" government is up to, and doubtless she uses the opportunity to ask pointed questions whenever necessary. Probably the one real power the monarch retains is to nominate the Prime Minister. Conventionally this is the leader of the largest party in the Commons, but she retains the right to ask anyone who can form a working government. The powers of the Crown are exercised by her Ministers, through the Civil Service, who are servants of the Crown, rather than the Queen, which is why they largely remain in post when the Government changes.

Both of these answers are right, but they haven't exactly hit the nail on the head so to speak. The Queen DOES IN FACT have some rather powerful political uses. She does call upon (typically) the Leader of the Party who maintains the most seats in the House of Commons. This is not to say however, that this Party itself has the majority of seats in the whole house. The Government of the United Kingdom, (As well as Canada, Australia and 14 other countries) have NO mechanism for starting or stopping the business of Government. No session of Parliament can start with out the Queen (Or in her other Realms, her Representative, Usually a Governor General) opening it via a Speech from the Throne, and the business of Government does not (technically) end until the Prime Minister goes to the Queen (Or, again, in her other Realms, her Representative, Usually a Governor General) to request that Parliament be disbanded and to request a writ be made to order a new election. One of the most important effects of this power, is that no bill may become law unless the Queen signs it. This effectively gives the Crown final say so over any abusive legislation that could harm Her Majesty's subjects. This use of Constitutional Monarchy ensures that any Government of the day is simply a "temporary holder" of the Crown's legal authority, and thusly, any Government who becomes too abusive of these powers can be removed with the stroke of a pen. Admittedly, something VERY BAD would have to happen in order for these powers to be used; but rare use of powers does NOT make them useless. http://www.danphilp.ca/maplekingdom

In the normal course of events, the monarch has plenty of influence but little actual power. However, in times of constitutional crisis, the monarch has significant power. The most likely scenario (it has happened before and will probably happen again) is that there is a "hung parliament" i.e. there has been an election but no one party has an absolute majority. The monarch has the power to decide whether to ask one of the party leaders to form a minority administration or to call another general election.