While US officials reportedly complained over the British move saying it has taken a unilateral decision, Chinese Foreign Ministry spokesman Hong Lei welcomed UK's move saying China will follow principles of openness and transparency.
The AIIB has an authorised capital of USD 100 billion and the initial subscribed capital of USD 50 billion.
India along with 26 other countries joined the bank as its founding members when it was formally set up last year by Chinese President Xi Jinping.
About US criticism that the new bank could be a rival to Japan-led Asia Development Bank (ADB) and the World Bank, Hong said the bank will follow the principles of openness, transparency, inclusiveness and fairness to design its governance structure and operational policies.
"It will learn from good practices of multilateral development banks and take detour from their path so as to reduce the cost and increase costs and operational efficiency," he said.
The AIIB will complement existing multilateral development banks, Hong said adding that it would better serve the member states and support the infrastructure building and economic development in Asia.
"A number of countries want to join and preparation are going on. We welcome all countries to join us," he said.
If all goes well, the UK will officially become a prospective member by end of this month, Hong said parrying a question what China had offered in return to get the prime western country like Britain to join the new bank, expected to be functional later this year.