If a Bill is amended in the Lords or Commons, and the Lords or Commons reject or change the other House’s amendments, it must return to the other House so it can endorse or reject the amendments.
Proceedings on the Consideration of Amendments are programmed as with all other stages. The Government tables motions agreeing or disagreeing with the Amendments. It may also move amendments in lieu of changes rejected.
Unless the other Chamber acquiesce with the alterations made by the other Chamber, the Bill will be passed back for their consideration. The Bill is communicated with ‘Reasons’, which outline why the Lower or Upper House does not agree with each other. Technically, these Reasons are drawn up by a Reasons Committee, which reports the Reasons and passes the Bill back.
If the other Chamber still cannot agree to the provision, they re-amend it and send it back (the Lords communicates with the Commons via ‘Messages’). The other Chamber will consider the changes and may again reject them or make further changes in lieu. The Bill goes back again.
In theory, this so-called ‘ping-pong’ can continue indefinitely until consensus is reached but this is limited by the availability of Parliamentary time, the length of the Session and the likelihood that one or other side will put forward an acceptable compromise. In most cases, if a Bill does not receive Royal Assent before prorogation, it is lost.