Once you have your MSc you will be eligible for any UK research council studentship, so funding will not be a problem. If you want to start you PhD in October you should already be looking as studentships can fill up fast. Part time PhD's in the sciences tend to be taken by university staff working as technicians or research assistants. In most cases a part time PhD will actually take the same length of time as a full time PhD. The difference between the two is usually only on paper. A part time student will usually be in the employment of the university and may have to work a few extra hours a week. They are generally better paid, but unlike full time students, will pay tax on their income.