There is
Cel-Fi which are at the moment the only approved relays in the UK AFAIK, but they are not cheap and look more aimed at small businesses looking to ensure mobile coverage in their offices.
You'll likely find searching on the internets some people selling active mobile/cell signal boosters (a lot of which are made in China) - unless you are certified by the network operator to install such a system, then they are illegal to operate in the UK.
There are also "femtocells" which are mini mobile base stations that are connected to your broadband connection to provide indoor coverage where a network cannot penetrate to. Only Vodafone actively sell these, known as 'Sure Signal' - EE, O2 & 3 also have these femtocells, but don't actively sell them. Instead you have to jump through at least a couple of hoops concerning your reception problems with the respective customer services before they may send one out to you to use. These femtocells are restricted to 3G phones (i.e. 2G only phones cannot use them) and are set up to limit the phones that can use them, so an unauthorised phone on the same network can't use it.
An alternative method if you are on O2 (contract customers only) or 3 is the ability to use their call & text services using a wifi connection - O2's name for this is TuGo while 3's is In Touch. However there has been a lot of mixed reviews over how well these applications work. EE have a "WiFi Calling" service that is better integrated into handsets, but is currently only available on a few premium handsets at present and for pay monthly customers only.
Finally, another plan is to use the phone as a form of 'relay' where you place the phone in a location at home where you can receive a steady signal (e.g. a upstairs bedroom window on the side of a house facing a mobile base station, even if it's just 1-2 bars of signal strength on your phone) and use an additional gadget to assist you. For calls, this can for example be the use of a bluetooth headset paired with the phone. If you have an Andriod OS phone and a tablet also running on Android you can also download apps for both which help set up forwarding calls & SMS messages from the phone to the tablet (and vice-versa e.g. compose a message on the tablet, it forwards it to the phone which then sends it to the network). As long as you can get some sort of a signal and a link can be maintained then this can act as a compromise in tricky circumstances.