Any group of people can meet to discuss a budget or anything else in the universe without agendas or minutes. But, for it to become an "official" meeting of a committee it would have to be advertised , and have an agenda , and would by law be open to the public (public bodies admission to meetings act 1960). Committees usually make recommendations to full Councils.
Also, There is Section 25(2) of the Localism Act 2011 which provides that a decision maker is not to be taken to have had, or to have appeared to have had, a closed mind when making a decision just because – (a) the decision maker had previously done anything that directly or indirectly indicated what view the decision maker took, or would or might take in relation to a matter, and (b) the matter was relevant to the decision.
In plain language, they can get away with it unless enough people disagree.