By Sean Curran
BBC Parliamentary correspondent
It is, by any standards, an unusual game of ping pong that ends with one player using a nuclear weapon.
Between now and Thursday we expect the Hunting Bill to be batted from the Commons to the Lords and back again as MPs and peers argue for and against a complete ban on hunting with dogs in England and Wales.
This "ping pong" is just one of the ways in which the two Houses mark the end of the parliamentary year.
The Parliament Act may be used to thwart peers' opposition to the ban
Ministers, anxious to get new laws onto the statute book, start by issuing blood curdling threats, and end by offering concessions.
Their Lordships promise a last ditch stand but, reluctant to push their luck too far, usually cut a deal at the eleventh hour.
Not this time though. If the Lords continue to reject the Hunting Bill the Parliament Act (or Acts to be accurate) can be used to thwart peers and force the bill through in spite of their objections.
The Parliament Acts are often referred to as the parliamentary "nuclear deterrent" - the mere threat that the rarely used powers might be used is usually enough to bring truculent dukes and earls into line.
Power to delay
The first Parliament Act was introduced by the Liberal Prime Minister, Herbert Asquith, in 1911 after Conservatives defied centuries of parliamentary precedent and used their majority in the Lords to block Lloyd George's "people's Budget" of 1909.
The 1911 Act - which was approved by both the Commons and the Lords - restricted the powers of the House of Lords to delay and block legislation.
From now peers would only be able to reject a bill for two years over three successive parliamentary sessions.
After that it could become law in spite of their objections.
New restrictions on the powers of the Lords were introduced in the 1949 Parliament Act which reduced the time peers could delay a bill from two years over three parliamentary sessions to one year over two parliamentary sessions.
Attlee era bill
This is the most controversial of the two Parliament Acts because it was never passed by the House of Lords.
Clement Attlee's Labour Government day had to use the 1911 Act to get the Bill onto the statute book.
Ever since constitutional lawyers have debated whether the 1949 Act - and therefore any law introduced as a result of the Parliament Acts - is valid.
The issue has never been tested in the courts but the Countryside Alliance has suggested that it might launch a legal challenge if the Parliament Acts are used to force through a hunting ban.
But we're getting a bit ahead of ourselves here.
At the moment the bill is still being debated by MPs and peers.
If by the end of the parliamentary year on Thursday, no final decision has been reached the Commons Speaker, Michael Martin, will have to decide whether the Parliament Acts can be used to pass the Hunting Bill.
The Parliament Acts can only be used if certain conditions have been met.
The same bill must be passed by the Commons in two successive parliamentary sessions.
There must a gap of one year between the Second Reading debate in the Commons in the first parliamentary session and the date the bill is sent to the Lords in the second session.
The bill must have been sent from the Commons to the Lords at least one month before the end of the second parliamentary session.
It must have been rejected by the Lords in both sessions.
If the Commons' Speaker can tick all the boxes on that checklist he can certify that the conditions set out in the 1911 Parliament Act have been met and the bill will then be given its Royal Assent.