Like going from silent movies to talkies at the end of the 1920s or going from black-and-white to colour TV in the 1960s, the switchover from analogue to digital TV is a major milestone in the history of broadcasting and for the more than 12 million or so people who live in the greater London area, this week is when this historic change will begin.

In 1999, the then culture secretary Chris Smith announced that the government's intention was to achieve switchover "between 2006 and 2010" but as with most projects of this size and complexity there has been a delay.

The digital switchover, as it has been branded, has been taking place across the UK since 2008 on an area-by-area basis and is scheduled to finish by the end of this year. However, for the biggest pocket of the population to be affected, those living in the capital, the next two weeks is when the switchover will take place.

For many, nothing will change, but according to Digital UK, the group which is overseeing the switchover, one million viewers are at risk of seeing blank TV screens once the analogue signal is turned off, beginning on 4 April.

In order to help those unsure of how this will affect them, we have put together a guide to help clear up any confusion, so you will know exactly what is happening and what you need to do over the coming weeks.

Digital Switchover: Why is it Happening?

Households in many parts of the UK are unable to receive digital Freeview services. Switching off the existing analogue broadcasting system will create the capacity necessary to extend this Freeview coverage to the whole country. Broadcasting in digital format is also a more efficient way to transmit television signals and will free up airwaves for new services such as ultra-fast wireless broadband, 4G services and mobile television.

Digital Switchover: When is it happening?

While the switchover has been taking place for over three years now in various parts of the UK, it has not come into effect in London yet, but that is all set to change from Wednesday, 4 April. On that day BBC Two will be switched over from analogue to digital, with the exact timing of the switch dependent on the which transmitter you are connected to.

The rest of the analogue channels - BBC One, ITV, Channel 4 and 5 - will then be switched off on 18 April. The two week delay is to allow those who are using analogue TV sets to make arrangements and switch over to digital. The change will allow Freeview coverage to reach more than 400,000 viewers than can receive it now in the region.

Digital Switchover: Do I have an analogue TV?

TV signals can be received via an aerial, satellite, cable or broadband connection. Switchover affects any TV that receives its signal from an aerial.

If you use an aerial, it will receive its signal from a transmitter. In the UK, there are more than 1,150 transmitters organised into around 80 transmitter groups that are switching to digital one by one. Each group has a main switchover transmitter and local relay transmitters. In London, the main switchover transmitter is located in Crystal Palace with 54 relay transmitters scattered around the capital.

Before switchover, local relay transmitters are only able to transmit an analogue TV signal. After switchover, for the first time, all transmitters including local relay transmitters will transmit a digital signal and increase the number of channels available from around 5 to around 15.

Where you live and which transmitter you receive your signal from will affect the number of channels you receive. Signals from nearby transmitters often overlap, so you may have a choice of which one you can watch. One may give you a better signal than another, or increase the number of services you can receive.

If you are watching a main transmitter you will receive more than 40 digital channels. If you are watching a relay transmitter you will receive around 15 digital TV channels. To check which transmitter you receive from, use the postcode checker on the Digital UK website.

Digital Switchover: What if I have Sky or TiVo

While there will be a lot of people affected by the Digital Switchover, for the vast majority, nothing will change. Those receiving there TV signal from Sky or Virgin Media will continue as normal with little or no change. Those already using one of the large large of Freeview boxes available should also see little change, though some may see an increase to the number of channels available to them which could require them to retune their set-top box.

For those still using the analogue service, there are three main options open to them if they want to convert to digital. The first is to sign up with a subscriber like Sky or Virgin Media, the second is to buy a set-top Freeview box to receive the new convert their new digital signal through their existing aerial and the final option is to upgrade their TVs to one with an integrated Freeview tuner, which most flatscreen TVs come with nowadays.

Digital Switchover: How much does digital television cost?

For many, nothing will change in terms of cost, as they will be getting their TV signal from sources such as Sky or Virgin Media and will be paying for the privilege already.

For those getting digital for the first time or those converting secondary sets around the home, the cost will vary according to the number of TVs and method of conversion. It's estimated that five to 10 percent of households may need to replace damaged aerials in order to receive Freeview signals.

  • Freeview digital boxes start from around £20
  • Digital televisions start from around £150
  • Freesat from Sky costs approximately £175 (includes installation)
  • Freesat from the BBC/ITV costs from £30 for a digital box, £450 for a digital TV.
  • Satellite dish installation (if required) from £80
  • Subscriptions (e.g. Sky, Virgin, Top Up TV) start from approximately £10 per month
  • Digital television recorders cost from around £80
  • A standard new roof aerial normally costs £60-180
A map of London, showing which areas will be switched from analogue to digital from 4 April.

Digital Switchover: What channels will be available?

The number of channels you will be able to receive will depend on your location but for most people it will be somewhere between 15 and 40. The channel line up will include all the main national broadcasters including BBC, ITV, Channel 4, 5 plus extra channels from each, inlcuding BBC Three and Four; ITV 2, 3 and 4; E4, More 4 and Film 4; 5USA and 5+1.

There will also be access to five HD channels from BBC, ITV and Channel 4 as well as music channels Viva and 4Music. News from Sky, BBC and Al Jaeera will also be available as will three dedicated childrens channels. There will also be 25 digital radio stations avialable.