The company’s turnover fell by 1.7pc in the second quarter and its profitability depends largely on controlling costs. The pension deficit is also a worry.

Overall, the City is positive. Thirteen of the 23 analysts monitored by FactSet Research Systems rate BT shares a buy, while just four say sell. The average price target is 209p.

If you bought British Gas shares in its famous “tell Sid” privatisation of 1986, you would now own a portfolio of three energy-related companies.

First, in 1997, it split into Centrica, the retail arm, and BG, its exploration business. BG then span off Lattice, the gas pipeline operation, in 2000. Lattice merged with National Grid to form National Grid Transco two years later, with the company later becoming plain old National Grid again.

Anyone who spent £135 on 100 shares in British Gas at privatisation would now own 100 shares in Centrica (current value about £294), 84 in BG (£1,123) and 31 in National Grid (£199). So their holding would now be worth a total of £1,616.

All three companies are seen as solid businesses. Centrica’s British Gas retail arm has been raising prices to maintain margins; BG has some highly regarded assets in Brazil; and National Grid is a reliable dividend payer.

Analysts at Evolution Securities said recent attempts by the Government to boost competition in the energy market were unlikely to have much impact on Centrica’s profits. The broker said its investment case – a buy rating and a price target of 376p – was based on the company’s “very powerful cash flow”. UBS rates Centrica a buy with a price target of 330p.

The City is very bullish about BG Group. Analysts’ average price target is £17.14, according to FactSet, with no sellers among the 28 brokers monitored; the vast majority – 26 – say buy.

National Grid, by contrast, is seen as a hold. This is the rating of 11 of the 16 brokers followed by FactSet; the average price target is 629p.

Centrica and BG could soon be reunited, according to recent stock market rumours. China’s Sinopec was said to have teamed up with Centrica to launch a £20-a-share offer for BG.

BA’s merger with Iberia may prove fruitful

New shareholders who bought into British Airways’ privatisation in 1987 saw their shares soar to an instant 80pc gain. The flotation was so popular that people who applied for 5,000 shares received only 250, leaving many bitterly disappointed. On the first day of trading the shares surged from the 65.5p issue price to close at 109p. They peaked above £7 in 1997.

Since then, the company has endured the shocks of September 11, health scares such as the Sars virus and the Iraq war, which all hit airlines hard, as well as the financial crisis. It has responded by merging with one rival, Spain’s Iberia, and co-operating with another, American Airlines.

The merged company, International Airlines Group (IAG), recently increased its estimates of the benefits (“synergies” in the jargon) of the merger by €50m (£42m) and set itself an ambitious target of making €1.5bn in annual operating profits by 2015 – more than three times the forecast €480m profits for this year.

It envisaged €150m in additional benefits from its tie-up with American Airlines and at least €100m from the creation of a new budget airline, Iberia Express.

Some analysts were sceptical. “These targets assume something rarely, if ever, achieved by an airline – retain merger synergies and cost savings for shareholders,” said Investec. “History is littered with examples of airline restructuring gains being competed away.

“Given the deteriorating economic outlook and substantial cost pressures, we are not convinced these targets will be even remotely achieved.” But the broker did praise IAG’s management team, which had an “infectious passion” for their business. “The former Iberia and BA teams have bonded and a strong management team has formed,” it said, putting a fair value of 100p on the shares.

UBS, the Swiss bank, recently cut its price target by 20p to 240p, although it maintained a buy rating.

The average price target among the 23 brokers monitored by FactSet is 199p. Twelve say buy, six hold and five sell.