Generally an employee cannot bring a claim for unfair dismissal until he has at least 2 years service. It was 1 year but the current Government increased it to 2 years as part of their campaign to boost employment! There are exceptions to this; any employee dismissed by reason of maternity, paternity, for raising health and safety concerns or for asserting a statutory right can bring a claim for unfair dismissal whatever their length of service.
To this list of exceptions will be added a dismissal which is related to the employee's political opinion or affiliation. This is not a voluntary move on the part of the Government but a response to an adverse judgment in the European Court of Human Rights.
Note that it only removes the service qualification. A dismissal for political opinions may still be fair. We have been through this in a series of cases, usually involving members of the BNP. Those cases were argued under a claim of discrimination for belief.
It seems to me that a dismissal for political opinion or affiliation may be fair where that opinion or affiliation is counter to the purpose of the employer- a member of the BNP being an employee of a left wing party perhaps, or causing substantial and prejudicial disharmony in the workplace.