For UK entry visa applications leading to settlement UKBA only requires a very basic level (A1) of the Common European Framework of Reference for Speaking and Listening. There is no reading or writing or grammar testing at all.
The minimum level of IELTS (General) is level B1 (score of 4) so already above the UKBA requirement.
You'll find that IELTS Academic at 7 and above are a requirement for many types of jobs related to your area.