LONDON, April 26 (Reuters) - British lawmakers on Monday called on the government to publish all communications with pharmaceutical companies to understand if private lobbying influenced its opposition to a waiver of intellectual property rules for COVID-19 vaccines. The United States and a handful of other big countries, including the United Kingdom, have blocked negotiations at the World Trade Organization (WTO) involving a proposal spearheaded by India and South Africa that now has the support of 100 WTO members. The proposal would temporarily waive the intellectual property (IP) rights of pharmaceutical companies to allow developing countries to produce vaccines. The waiver is opposed by the U.S. Chamber of Commerce and big pharmaceutical companies such as Pfizer PFE.N, BioNTech 22UAy.DE, Moderna MRNA.O, and Johnson & Johnson JNJ.N. A cross-party group of UK lawmakers has signed a statement calling for Prime Minister Boris Johnson, ministers, and senior civil servants to publish all email, text, and WhatsApp messages exchanged with pharmaceutical companies and their lobbyists. Patient advocacy and vaccine equity organisations have also signed the statement, including Global Justice Now, Just Treatment, StopAIDS, Frontline AIDS, Universities Allied for Essential Medicines UK, Students for Global Health, and Nurses United UK. "The UK"s opposition to an intellectual property waiver on COVID-19 vaccines is utterly indefensible," said Heidi Chow, senior policy and campaigns manager at Global Justice Now, which organised the joint statement. A spokesperson for the UK government said it prioritised transparency but stakeholders had a right to expect a reasonable degree of confidentiality in their communications. The UK was one of the biggest donors to Covax to ensure global access to vaccines and continued to encourage manufacturers to provide their vaccines on a not-for-profit, transparent basis. "We are committed to exploring ways in which we can improve equitable access further and believe this should be done through the existing Intellectual Property framework," added the spokesperson. Last week U.S. lawmakers and nonprofit groups heaped pressure on the Biden administration to back the patent waiver ahead of the next formal WTO meeting on the issue on May 5. ((Reporting by James Davey; Editing by Alexandra Hudson))