For all employees employed on or after 6th April 2012, the qualifying period for unfair dismissal (and requests for a statement of reasons for dismissal) increases to two years. Employees whose period of continuous employment began on or before 5th April 2012 will still be subject to the one year qualifying period.
The current government claims that this will encourage employers to hire staff as it will give them longer to decide whether it was the right decision to recruit someone in the first place. Aside from the knock on effect this change is likely to have on the economy (less security for the working consumer means they are less likely to spend their money) it is doubtful whether this will have the effect the government hopes.
Employees who fall short of the qualifying period will often try and include a discrimination or whistleblowing claim to get around this (there is no minimum period of employment necessary to pursue these claims). It is notoriously difficult to have claims struck out at an early stage in employment proceedings as the tribunal often cannot reach a decision on a claim without hearing evidence.
Discrimination and whistleblowing claims are far more costly to defend (and in a lot of ways harder to predict) than a straightforward unfair dismissal claim.