Hi,
I have copied the following from the Metrpolitan Police website.
You could pass this info onto the person who wants to buy the rifle, and when he gets the licence, plus a Firearms Certificate, you could go ahead with the deal.
Hope this helps.
http://www.met.police.uk/firearms-enquiries/faq7-8.htm
To permanently import or export firearms will normally require the grant of a licence from the Department of Trade and Industry. The import and export of firearms is a complex subject and advice should be sought from the following:
Import Export
Department of Trade & Industry
Import Licensing Branch
Queensway House
West Precinct
Billingham
TS23 2NF
tel: 01642 364351
fax: 01642 364269
For more information on importing firearms, visit the the Foreign Commonwealth Office website.
Department of Trade & Industry
Export Licensing Unit
4 Abbey Orchard Street
London
SW1P 2HT
tel: 020 7215 8070
fax: 020 7215 0558
e-mail: eco.help@dti.gsi.gov.uk
For more information on exporting firearms, visit the Department of Trade and Industry Export Control web-site.