Doing work on the gas system in your own home is not if you are competent.
competence is having a level of skill, knowledge and experience to carry out a task professionally and safely without causing risk or harm to people or property. The fact that you are here asking questions means you do not fall into this category. Having the correct information to carry out the task DOES NOT make you competent and thats why no one is giving it to you. The very fact you think its just ok to Tee into a gas supply to one applianec appliance to add another shows how ill thought out your idea is and how little you understand. Clearly you will carry on regardless so I just hope for other peoples sake, who live around you that it isn't a disaster.
On another point you seem to have alienated every qualified gas engineer here by claiming we are all rip off merchant charlatans out to make a quick buck. Oh and by the way its not Corgi anymore its Gas Safe, Corgi is gone.
Its hardly surprising really that you've had idiots in your house when your obviously such a tightwad. Quality gas fitters/engineers/blokes/whatever don't work for tightwads, we suss them on the phone, we haven't got the time/patience to negotiate over price to service your boiler, or compete with 7 other people to fit your hob, we've got better things to do and better customers to serve who appreciate the work we do for them and are happy to pay a fair price for a quality job and not argue over price.