London's transport bosses are telling travellers on the tube system to beat the heat by carrying a bottle of water with them when they venture underground.

But how many of us are refilling our bottles with tap water rather than pouring money down the tube -- not to mention the cost of recycling the plastic bottles -- by buying a new bottle of water each day?

Cue the National Hydration Council whose eye-catching advertising campaign to encourage people to buy more "naturally sourced bottled water" -- on health grounds -- featured prominently on the underground network earlier this year.

The worrying thing for the bottled water lobby is not that people are doing what would appear to be the most sensible thing and refilling their bottles from the tap, but that Britons are replacing bottled water with sugary drinks instead.

We're told that sales of bottled water fell by 7 percent last year, with 71 percent of that decline the result of people buying sweet drinks instead. Good news for the soft drinks industry perhaps, but a worry for health officials.

Meanwhile, beneath the streets of London, the hot and flustered faces of fellow tube passengers shows just how dire it is on board the capital's underground trains when the mercury rises.

With a decent air-conditioning system on most lines a distant prospect, Transport for London (TfL) could show it cares by offering each of its cash-strapped passengers a free TfL water bottle and the opportunity to refill them at its stations.

Spring is making a cautious appearance in London now and with it a growing number of cyclists are venturing out onto the streets of the capital.

I also noticed, as I rode south towards the Smithfield meat market last week, another less welcome sign of the season — a ghost bike. This one had only been there for a few days.

The ghosts are white-painted bikes chained to a railing or a lamp post near where a cyclist has died in a traffic accident. I’ve spotted a few of these rather grim memorials in London, and they can also be seen in other cities in Britain and around the world.

Cycling has become more popular in London, perhaps because people want to do something for the environment, and also perhaps to escape the bombers after the city’s public transport system was struck in 2005. But as the ghost bikes show, there can still be a price to pay.