For the purposes if this i'll ignore the obvious questions of "why would they do that?" and "how could Britain suddenly start ruling vast new territories again?".

But to the two countries you mentioned, no there isn't. The UK recognises both as fully independant sovereign states and holds no claim over either their governance or their territory. The Foreign Office also lacks any plans as to what it would do if this request was made. Legally it's the same situation as it would be if Mongolia, Brazil or any other state that was never under British rule requested to be a colony.

The closest you could get is with some of the former colonies that still retain the queen as head of state. For example, royal assent for the bills passed the Australian Parliament is given by the governor general before they become law. Its technically possible for both the Australian and UK Parliaments to vote to repeal the 1986 Australia Act and the 1931 Statute of Westminster etc, which would see Australia revert to its pre independence status. Really the water is very muddy around these issues though, the Australia Act was passed by both Parliaments because no one was really sure which Parliament was ultimately sovereign in this issue.

Britain retains ties with its former colonies through the Commonwealth, which is a voluntary organisation. The queen is head of this, but its not the British Empire. All the members are equal sovereign states, and there are some members such as Mozambique which were never part of the British Empire at all.