Royal Mail will be sold off but how did other privatisations go? (Reuters)

Privatisation defined Margaret Thatcher's premiership but even the matriarch of free-market economics winced at the idea of selling off the historic Royal Mail. The former prime minister reportedly said she was not "prepared to have the Queen's head privatised".

Just five months after Thatcher died and among a barrage of controversy and criticism, the current Conservative party leader, David Cameron, is to oversee the sale of the state-owned employer.

The government has argued that the flotation will help ensure the "long-term sustainability of the six-days-a-week, one-price-goes-anywhere, universal" postal service. Detractors, such as shadow business secretary Chuka Umunna, have argued against it.

Whatever your opinion, it is inevitable that the move will be judged against previous privatisations, including British Telecom, British Airways, British Rail and British Gas. IBTimesUK takes a look at how these organisations were sold off and how they fare today.

British Gas

"If you see Sid...Tell him!" TV sets boomed in 1986. The catchy ad campaign was introduced to encourage people to buy shares for the soon-to-be privatised British Gas Corporation (BGC), following the introduction of the Gas Act 1986.

On the morning of 8 December, 1986, British Gas - the grandiose "corporation" now dropped from its name - floated on the London Stock Exchange for 135p per share amidst a £9bn bonanza sell-off. Its initial price offering (IPO) was the highest of its time and prospective shareholders could pay for a stake in the business with instalments of 50p, 45p and 40p.

British Gas, 11 years after its sell-off, demerged to form two separate organisations: Centrica and the BG Group. The closing share price of the two employers on their first of day trading was 64.25p and 173.25p, respectively.

BG Group, a multinational oil and gas company, boasts a £5bn profit before tax and gave a full-year dividend per share of 16.67p. Centrica, a multinational utility organisation, recorded £2.7bn profit before tax and granted a full-year dividend per share of 16.4p, according to their 2012 annual reports.

British Telecom

BT was the first large - and so probably the most controversial - government-owned employer to be sold off, following the passing of the Tories' 1984 Telecommunications Act. The flotation saw more than half (50.2 %) of the communication organisation's shares being sold to the public.

Today, according to its 2013 annual report, BT has a £2.5bn profit before tax and a full-year dividend of 9.5p. The company recently expanded into the competitive world of sports broadcasting, with new channel BT Sport airing Premier League football games and other spectacles.

British Airways

BA still has the patriotic pressure of flying the union flag but the organisation was finally privatised in 1987 in an oversubscribed flotation. The airline received more than one million applications for shares at 125p a pop. It made more history in the same year when the first women pilots for BA were hired and the company merged with financially troubled rival British Caledonian.

BA, which is now part of the International Airlines Group, which faces stiff competition from the likes of Richard Branson's Virgin Atlantic and budget competitors. It posted a £139m operating loss before tax, according to its 2012 annual report, and the directors decided against a dividend.

British Rail

Due to losses, heavy dependencies on state subsidies and a need to prioritise safety, British Rail was privatised over three years, between 1994 and 1997. In 1994, the ownership and infrastructure of the track passed from the state-owned company to operator Railtrack, which was subsequently privatised in 1996.

Britain's rail infrastructure was owned by the organisation until 2002 when Railtrack, still recovering from its failings around the Hatfield train crash, was reconstituted as Network Rail. But now with rising rail fares and a wave of customer discontent, calls to renationalise the railways have become louder.