Progress made on Irish border backstop but time is of the essence - UK's May

(Adds detail, quotes)

LONDON, Feb 20 (Reuters) - British Prime Minister Theresa May said on Wednesday that progress had been made in solving the impasse over the backstop arrangements for the Irish border that has hindered her Brexit deal but added that time was running out to secure changes.

May is in Brussels seeking to change the agreement she struck with the EU last year, after the deal was heavily defeated by British lawmakers.

Lawmakers in May's Conservative party have criticised backstop arrangements to avoid a hard border in Ireland (Other OTC: IRLD - news) , saying that under the current deal it could lock in EU rules for Northern Ireland indefinitely.

"I've underlined the need for us to see legally binding changes to the backstop that ensure that it cannot be indefinite. That's what is required," May told international broadcasters after meeting European Commission President Jean-Claude Juncker in Brussels.

May said that negotiations with the EU would contine "at pace."

"Time (Frankfurt: A11312 - news) is of the essence, and it's in both out interests that when the UK leaves the EU, that it does so in an orderly way. So we've made progress."

Earlier in the day, three pro-EU lawmakers quit the Conservatives, criticising her approach to Brexit in an illustration of the tensions in May's party.

They believe there should be another referendum on May's deal, while some Eurosceptic lawmakers in her party believe Britain should leave on March 29 even if it means leaving without a deal.

"The question of our membership of the European Union has been a matter of disagreement in our party for many years now and it was never going to be easy for the UK to leave the European Union after over 40 years of membership," May said.

"But I believe that by delivering on the result of the referendum... we’re doing the right thing by the country."

(Writing by Alistair Smout, Editing by William Maclean)