The answer to your first question is "Yes he can"! Under devolved school management (DSM) the headteacher gets at least 80 per cent of the money needed to run the school and this includes not only money for staffing, the rates, heating, books and equipment, but also a certain amount for furnishing. Within the constraints of providing a "proper" education, the headteacher is free to transfer money from one area of spending to another according to what he or she - and the staff - see as the priorities.
In these times of cutbacks, many headteachers use their furniture budgets for books and equipment. I know of cases where the entire furniture budget has been transferred in this way. However, the headteacher has responsibility for those areas of spending for which heshe has been provided with a budget. At some point heshe will have to recognise the need to spend money on furnishings, and replacing the carpet in the head's office may well become a priority, as may buying some new chairs for the classrooms. There is, therefore, nothing to stop the headteacher transferring money into the furnishing budget from some other area of spending.
The answer to your second question is "No"! At the time when the DSM guidelines were being prepared, school boards were consulted on the level of control they wanted to have and the almost universal message given to the Government was that school boards did not want to control all these extra budgets. The result was that boards retain their right of approval over the headteacher's plans for spending money on books and equipment, but in other areas of spending the head is in control.
Heads are meant to consult over all spending proposals and they have devised different ways of doing this. Many follow the spending proposals implied in the school development plan. Others have set up finance committees which may include the chairperson of the board. And yet others undertake specific consultations over specific proposals.
Of course a headteacher has little option on how heshe spends the bulk of the money. There is no choice, for example, over paying the rates or staff salaries, although it is sometimes possible to trade a teacher for extra support staff. The true area of flexibility is very limited and this is why a major purchase in one particular area will usually require a transfer of funds from another area - whether it's carpets or new computers.
There is another consequence of DSM: authorities cannot put extra money into a school with complete confidence that it will be spent how they intend. Suppose, for example, an authority increases the staffing budget slightly, meaning it to be used to set up a supported study scheme. The headteacher may decide that the school's main need is for extra computers - and spend the money accordingly.
Because it is much more difficult for an authority to direct a headteacher's spending, developing these desirable projects will require the agreement of the headteachers which in turn means a lot more time spent on consultation. Maybe DSM is desirable, but it is certainly more expensive and, as have often been said, "change" means "different", it does not necessarily mean "better".