BRUSSELS (Reuters) - The European Parliament could block a Brexit deal for Britain if EU leaders exclude lawmakers from the negotiating process, its outgoing speaker warned on Thursday as the legislature pushes for a bigger role in the talks.

European Parliament President Martin Schulz delivers a speech on his end of term as President, ahead of a voting session at the European Parliament in Strasbourg, France, December 14, 2016. REUTERS/Vincent Kessler

“If we are not adequately involved, we may not be able to give our consent,” Parliament President Martin Schulz told an EU summit, according to a text of his remarks. “And in this situation the UK would face the hardest Brexit possible.”

He was reacting to a negotiating plan which Britain’s 27 EU partners are to agree later in the day. Parliament must ratify any deal needed to ensure an orderly Brexit. Schulz later said he feared Parliament might be so split that anti-EU British members from UKIP would be able to cast the decisive votes.

Taking a dig at European Council President Donald Tusk, Schulz said: “Tusk until today has not yet understood the European Parliament is not an obstacle, but it is a partner on the same equal footing like the other institutions.”

Institutional rivalries are part of Brussels politics and Parliament has long irked governments by trying to expand its powers. However, the squabbling highlights the difficulties the EU may have in maintaining a common front towards London.

Under the draft EU plan, seen by Reuters, the executive European Commission would run negotiations, under guidelines set by the Council of member states. Their representatives would “participate in a supporting role in all negotiation sessions”.

The Parliament would merely be kept “closely and regularly informed throughout the negotiation”.

The Commission’s negotiator is Frenchman Michel Barnier.

A senior EU official involved in planning a process which British Prime Minister Theresa May says she will launch by the end of March said lawmakers would give their input regularly.

“But in the negotiations proper, this is not for the legislature,” he said. “We have a Union negotiator, we need to show we trust him, otherwise he will be a weak negotiator.”

Nonetheless, Schulz later told reporters he believed leaders would amend their final plan.

On Wednesday, former Belgian premier Guy Verhofstadt, who is Parliament’s point man on Brexit, said he could launch separate talks with London if the Council freezes him out.

Verhofstadt, who proposes giving Britons “associate EU citizenship”, said he had a “useful meeting” on Thursday with May: “European Parliament and UK will work closely towards a fair agreement in the interest of all EU citizens,” he tweeted.