Parliament must have on-going involvement in the Brexit negotiations, Labour has warned as the Bill triggering withdrawal from the EU goes before the Lords.

Leader of the opposition in the upper house, Baroness Smith, insisted there would be no "extended ping pong" with amendments shuttling back and forth to the Commons, but peers would demand changes to the legislation.

Lady Smith told BBC Radio 4's Today programme concessions offered by the Government to help get the Brexit Bill through the Commons must be explicitly written into the legislation.

"The Government did make some concessions. I would like to see some of those concessions, like having a meaningful vote at the end, like having some parliamentary engagement throughout, on the face of the Bill."

Lady Smith said Parliament must have a say in the final Brexit deal.

"If the Government are saying 'we don't want a deal, we want longer engagement', or whatever. Parliament should be engaged in that process.

"If there is this ongoing parliamentary engagement, all of us can get involved in this. Waiting for two years' time is the wrong thing.

"It can't be we say to Theresa May 'bye by, off you go come back in two years with a deal', that's not good enough.

"All the House of Lords can do is ask the Commons to look at an issue again. I don't see any extended ping pong on this at all."

Before Brexit talks begin, the legislation allowing Mrs May to trigger Article 50 needs to clear Parliament, where the House of Lords will begin a marathon debate on Monday amid warnings peers are ready to rewrite the Bill.

Around 190 peers are expected to speak during the two days set aside for the European Union (Notification Of Withdrawal) Bill's second reading debate in the Lords, the first time the upper chamber will debate the legislation.

Former European commissioner Lord Mandelson has urged his colleagues not to "throw in the towel early" in the fight with the Government.

Labour and Liberal Democrat peers have indicated they are ready for battle, with efforts likely to focus on guarantees for EU citizens' rights and the ability of Parliament to have a meaningful vote on the final Brexit deal.

Votes are not likely at this stage, with efforts to force through amendments likely to come later in the Bill's passage through the Lords.

Once the two-year countdown to Brexit begins after the triggering of Article 50, which Mrs May has vowed to do by the end of March, the negotiations with the EU can commence, but the Prime Minister has been warned they will not be straightforward.

Lord Hill, who resigned as the UK's EU commissioner after the Brexit vote, told the BBC that Britain needs to show consistency and clarity in the negotiations.

"I think the idea that at the end of that process of negotiation, a British negotiator says 'Oh, I'm terribly sorry, that deal that I've just offered you, and struck with you, I'm afraid that Parliament have just voted on it and have changed the terms' - I don't see how we can negotiate in good faith if we were to proceed on that basis."

The peer criticised recent comments by former PM Tony Blair that politicians should campaign for the UK to be able to change its mind on Brexit.