The Lib Dems have not provided an estimate of the cost of their proposal, which would far exceed the billions being spent on the planned replacement for Trident.
France, the only other European country with nuclear weapons, has always maintained a fully independent system.
The Lib Dems say France's approach proves a sovereign British capability is achievable.
They argue it could be done in two stages - developing a way to maintain the existing Trident weapons system domestically, and in the longer term manufacturing a fully British-made replacement.
The party has traditionally been split on the issue of Britain's nuclear weapons.
Many in the party have campaigned for multilateral disarmament - something party sources insist they still believe in, while saying they must reflect the reality of the global situation.