If you are the Sole Proprietor of your business, as I am, then the money in your company bank account legally belongs to you in its entirety. If you are a Partnership different rules apply.
If the SIPP is in your own name, then contributions should be funded from your personal bank account from money which you have earned and transfered from your company account.
In order to gross up your pension contributions by 20% the pension company uses your NI number and cross checks on your personal self assessment tax return.
Remaining 40% or 50% tax relief is then claimed back via your tax return at year end.
Unless I am missing something I dont think there is any tax advantage in paying your SIPP from your company account, however I would be happy to be proved wrong.

Thanks for the responses everyone, I was unsure if it could be problematic (more for audit trail purposes) that 'member contributions' were coming from a company account, but I realise now that it isn't.