Urgent questions were raised in parliament ahead of a January 20 government deadline for a decision on the planning proposals for a new embassy.

The Daily Telegraph said it had obtained unredacted plans for the vast new building set to be erected close to the Tower of London on the historical site of the former Royal Mint.

It showed that Beijing reportedly plans to construct a single "concealed chamber" among "secret rooms" underneath the embassy which would be placed alongside sensitive underground communications cables.

Beijing also plans to demolish and rebuild a wall between the cables and the embassy, according to the unredacted plans.

The embassy, which if approved would be the largest in the UK by area, has been beset by delays, protests and concerns for years, prompting frustration in Beijing.

Alicia Kearns, the opposition Conservative Party's interior spokeswoman, told parliament Tuesday the new embassy would give China a "launch-pad for economic warfare" against Britain.

"The government can claim today that they had no idea about these secret rooms, and we will take them at that word," she said.

"But they cannot now say they have no power to protect us. Protect our economy, protect the British people, deny the Chinese Communist Party their embassy."

In response, planning minister Matthew Pennycook said the government would not be commenting on speculation in the press about the secret rooms and said the government had "transparently sought" further information on the redacted drawings.

"If new, potentially relevant information is drawn to the department's attention, it will be assessed," he said.

Kearns and other MPs also raised other security concerns, such as whether exiled Hong Kong activists living in the UK could face increased surveillance.

"We recognise that China poses a series of threats to UK national security and we challenge these robustly," Pennycook added.

"China also presents opportunities to the UK as the world's second largest economy and the UK's third largest trading partner. We will therefore continue to develop a consistent and pragmatic approach to economic engagement without compromising our national security."

Activists plan to protest against the proposed embassy on Saturday.

"I want my government to stand up to bullies, not reward them," said Labour MP Sarah Champion.

"We need to be seeing rules, limits, put in place around China to stop this behaviour, not rewarding them with the embassy that they so dearly want."