How to get a gas supply to your house

I prepared the below as a summary of what I have found out about getting a gas supply to my house, which is more than 23 metres from the gas main. I'd welcome any corrections, elaboration, or constructive criticism.

Note that there is some indication that you may save money by getting the trench dug yourself or by independant contractors.

The National Grid (formerly Transco) are not the only people who can provide a gas supply. A gas supply can be installed by any of 1 to 6 below (although not all of them will do it). It is probably best to get quotations from several different companies at the same time, since quoted prices typically vary very substantially in my experience.

1) National Grid
http://www.nationalgrid.com/uk/Gas/Connections/domestic/
For eastern england, for example: http://www.nationalgrid.com/uk/Gas/Connections/domestic/ee/connections.htm

2) Licensed Gas Supplier
These seem to be companies like British Gas, E.On, EDF, NPower, Scottish Power, Seeboard, Swalec, etc.

3) Utility Infrastructure Providers (UIPs)
Online form starting here http://www.nationalgrid.com/uk/Gas/Connections/CompetitiveQuotationForm/index.htm which is said to send out quotation requests to the several UIPs for you. Currently (Thursday 15 May 08) there is a message: "This facility is currently not available due to technical problems. It should be available as normal tomorrow." But it said that yesterday as well on Wednesday 14 May 08! Perhaps they are trying to push people towards Fulcrum which they wholely own, and who seem to be rip-off artistes in my opinion.
A list of some UIPs: http://www.sbgi.org.uk/uip
Another list of UIPs: http://www.lloydsregister.co.uk/girs.html

4) Independent Gas Transporters
Some information: http://www.nationalgrid.com/uk/Gas/Connections/IGT/
A list of contact details for IGTs http://www.energylinx.co.uk/independent_gas_transporters.htm

5) Owner/occupiers laying gas supply
http://www.nationalgrid.com/uk/Gas/Connections/uip2/uipoverview.htm
"Under the requirements of the Gas Act 1986 (as amended 1995) the owner/ occupier of premises has the right to provide and lay their own gas supply, to have that gas supply connected to National Grid's network and, if fit for purpose, to offer ownership of the pipe(s) to a Gas Transporter (GT) such as National Grid."
Not absolutely certain if this requires the owner/occuper to register as a UIP or not. If so, it is complicated: http://www.nationalgrid.com/uk/Gas/Connections/uip2/reg+uip.htm

6) In-filling
If all houses in an area are without mains gas this is known as an "in-fill" and also has different procedures, which I have not investigated fully yet, but it may be cheaper as the gas company may only charge you your share of the cost.

Energywatch
If the quotations seem unreasonable then you can get them reviewed by making a complaint to Energywatch, who will also answer general questions by email in addition to the bank of questions here: http://www.energywatch.org.uk/your_questions/index.asp