Sources close to the BBC said the construction contract would be worth at least £400m, including the design fees. The contract is thought to be split evenly between the shell and core – worth about £230m – and the fit-out, which has yet to be finalised.
A source said: "It is like a two-stage contract. The shell and core has been agreed and the fit-out will be sorted out at a later date."
Sources close to the BBC said it had already spent upwards of £50m on the scheme, which has been on site for nine months. The money will be paid back through the bond.
This way of funding the scheme, which will be handled by bank Morgan Stanley, will come as a surprise to the market.
The shell and core has been agreed and the fit-out will be sorted out at a later date
BBC property partner Land Securities Trillium, which is backing the White City studios scheme in west London, was expected to fund the Portland Place plans, but is acting solely as development manager, for which it will receive a fee.
A Land Securities spokesperson said: "In partnership with the BBC, we looked at all options with the corporation and this seemed the most commercially sensible route."
A source close to the BBC said the change in financing would not affect the construction programme but had allayed fears that it would not be able to continue paying for it.