Invoicing customers for work outside company SIC code

[KevinJackson]

Lets say we have John who is in the business of selling IT equipment. Based on what he sees in
companieshouse
his SIC is 46510 and he happily has registered a company under this SIC. Lets assume John is a jack of all trades and he is also a qualified plumber as well as a qualified Electrician. Proper "jack of all trades".
Should John register 2 more companies simply because the nature of his other professions [Plumbing] and [Electrician] are completely different from each other

OR

Use his IT business and simply invoice the customers under his IT business? Wouldn't it be odd to have an invoice for fixing a boiler under the name of a computer store?

What is the correct and legal way of doing above to minimise paper work and unnecessary registration of different companies?

 

[STDFR33]

One company can be used.

As far as I am aware, the SIC is used for statistical purposes and you should just pick the best fit.

There may be other important factors why using one company is not a good idea and you should speak to your accountant to see what is best.

 

[dotcomdude]

What is the correct and legal way of doing above to minimise paper work and unnecessary registration of different companies?

Change the company name to something a bit more vanilla...

 

[KevinJackson]

One company can be used.

As far as I am aware, the SIC is used for statistical purposes and you should just pick the best fit.

There may be other important factors why using one company is not a good idea and you should speak to your accountant to see what is best.

Could you elaborate on what other factors might persuade John to change his business model? What issues do you have in mind? Legality of the business or tax inefficiency?