I have been in contact with Wessex Pictures to get prices for the various items which Wally used in last night's demonstration.
The backing board appears to be Corri-Cor Mk III, which is £2-70 + VAT per sheet. There are volume discounts available, but the person to whom I spoke was unable to say what they are.
http://www.wessexpictures.com/product1680.htmlNubord was also suggested at the same price, but this is not listed as having the same archival properties.
http://www.wessexpictures.com/kraft_lined_board.htmlDouble sided tape is £2-70 + VAT per roll for 1/4" and £3-85 + VAT for 1/2".
http://www.wessexpictures.com/product584.htmlStandard brown masking tape is £1-55 for 1", £2-35 for 1 1/2", £3-10 for 2" and £4-20 for 3". All prices ex VAT.
http://www.wessexpictures.com/product576.htmlTesa brown masking tape is £4-60 for 1", £6-96 for 1 1/2" and £9-14 for 2". As before, all prices are ex VAT. It is unclear what the difference is between the Tesa product and standard masking tape in terms of quality, but I have been using the latter without any issues.
http://www.wessexpictures.com/product607.htmlIf anyone wants to add any of these items to our order, it will help reach the £75 total at which delivery becomes free.