From 13th April 1995 a new statutory medical test has applied throughout the Social Security system whenever a medical test of capacity for work is required (Social Security (Incapacity for Work) Act 1994, ss.5-7). The main benefit affected is Incapacity Benefit (which replaced Sickness Benefit and Invalidity Benefit as from 13th April 1995).

The new medical test does NOT normally apply in relation to the first 28 weeks of sickness nor in relation to Statutory Sick Pay (''SSP'') or industrial injuries disablement benefit (see s.171G of the Social Security Contributions and Benefits Act 1992, added in 1994).

The Department for Work & Pensions has issued a Guide for Medical Practitioners which contains the rules and background information about sickness certificates etc.

A Medical Appeals Tribunal hears appeals (reg 38 Social Security (Adjudication) Regulations 1995, SI 1995/1801).

Unless there is some reason to doubt the genuineness of a doctor's sickness certificate, an employment tribunal will accept a medical sick note as being proof that an employee was genuinely off work by reason of illness (MerseyRail Electrics 2002 Ltd v Taylor, EAT on 18th May 2005).

After lengthy consultation, proposals to replace doctors' "sick notes" with "fit notes" are in effect from 6th April 2010. As from that date the various forms of workers' sick note (also known as a medical certificate or a doctor’s statement) are replaced by a single new form of fitness for work medical certificate or "fit note". The general idea is that the new form of "fit note" will enable doctors to say a person may be fit for some work rather than simply that they are not ready to resume normal work. As from 6th April 2010 the "fit note" form for claiming health related social security benefits has the same wording as the fit note form for claiming statutory sick pay (''SSP'') from an employer.