Don't know, but have been invoiced by companies in UK and the VAT was exempt because we were both VAT registered. some cross country deal. pretty sure people in AAM will know alot more about than me.
I am in similar situation and I was advised that no Vat is payable. However your invoice must contain both your and their VAT numbers and must contain the following statement:
"No VAT is included in this invoice. The customer is responsible for accounting for the UK VAT chargeable on the supply on a reverse charge basis"