I will have been living in the uk 3 years by this october, and am planning to settle here. I would like to know whether this would preclude me from any of the resident studentships starting in October?
If you have been resident for reasons other than fulltime education you should be eligible. A full description of the eligibility criteria used by UK research councils can be found in the BBSRC studentship guide.
You can check by contacting the international or graduate office of any UK university.