Price difference for foreign BA account

[samsacker]

Hi all
Question: my friend has a companion voucher with BA.
They moved to the UK years ago – their BA account is registered in Bahrain. Trying to use the company’s voucher – it keeps quoting the price in Bahrani Dinars and it’s higher than the cost in the UK. Case in point – flight to Mexico is 30k Avios and £75. But in BHD dinar it’s the same Avios but the cost is £200 (per person)
How can we get the UK GBP cost on the account (I.e. down to 75) ??
Thanks

[BA Flyer IHG Stayer]

They need to have their UK address in their BAC account