The new subs, beginning in 2028, will replace the Royal Navy's Vanguard submarines now in service.
"The UK has been committed to a continuous at-sea deterrent for more than 45 years," said Defense Secretary Michael Fallon. "This is because it is the responsibility of the British government to protect its citizens and provide this vital line of defense. It is therefore crucial that we continue to invest in the Successor program to be ready for a final decision on renewal next year."
"It is thanks to our long-term economic plan that we are able to invest in this latest wave of design funding, which will help to secure the jobs of hundreds of people working across the MOD's three main industrial partners working on the Successor program. This underlines how important this work is to the British economy as well as the future security of the UK."
According to Tony Johns, BAE Systems' managing director for submarines, the funding will enable the company to mature the submarine's design over the next year to begin construction in 2016.
"Today's announcement on the third phase of design funding is another step forward in the program to deliver the Successor submarine," said Chief of Materiel (Fleet) Vice Adm. Simon Lister.
"Over the next year, work on the design of the submarine will draw on cutting edge capabilities in innovation, design and engineering available in the UK to ensure we are able to meet the future defense needs of the UK."