What is the difference between a Project and a Programme?

I am always being asked what the difference is between a Project and a Programme and whilst there may be lots of debates around this the answer is quite simple.
The debates are usually around the kudos of a programme (and the title of Programme Manager) over a project however, many projects can be far more complex than some programmes, and can control budgets far greater than that of programme.
A project is a temporary organisation setup to deliver a benefit to the business whether it be additional profit, compliance or improved efficiencies. Projects deliver benefits of which it needs all its workstreams to deliver for the business to deliver the benefit.
Whereas a programme has two or more projects which can be deliver business benefits independently, however these are intrinsically linked and the desire of the business is for the benefits to be delivered and managed together. Generally there will be functional workstreams such as IT & Business Readiness which run alongside the projects to support the delivery of the projects.

For example the implementation of a new ERP system could involve millions of pounds worth of investment last several years and involve most areas within a business however; the delivery of the ERP system has to be delivered as a whole to deliver the business case.
In another example a company wish to setup a programme to reduce their telephony costs, this could involve two projects, one for landlines and one for mobiles, working with the same or a different provider. This may only save the company ½ million pounds and involve just a few areas within the business however; the delivery of either of the projects will deliver a benefits to the business.

So in answer to the question, what is the difference between a project and a programme, is not necessarily the size or complexity but, it is based around the business case and whether elements of the business case can be delivered in isolation.