You will know that to sue is to make a claim for a remedy in the civil courts by issuing proceedings.
This is very easy to do either with a solicitor or without, if you intend to use a solicitor try to find a firm who offer a Conditional Fee arrangement (no win no fee, if your claim is one they can deal with), this will be a good test of the strength of your position as it will only be accepted if it has a very good chance of success. If you do not intend to use a solicitor, and I would suggest you do, go to the civil court dealing in your area of concern and ask the staff to provide the information, they will not give legal advice.