Interestingly the current BS7671:2008 "Wiring Regs" does not specifically lay down frequency of testing of fixed installations.
It is the IEE's 'Guidence Note 3 - Inspection and Testing' which lists a large number of occupancies and which says the Launderettes should be tested yearly. There are cross references to both the Electricity at Work Regulations and the Electricity, Safety, Quality and Continuity Regs. I think it is the former Regs (Regulation 4 and Memorandum) which may be the legal requirement.
So if you haven't complied with statutory requirements could that be a get-out for the insurer?
(By the way, the new version of BS7671:2011 17th Edition with Amendment 1 is to be published this month. Taking effect from 1st Jan 2012, the 'Periodic Testing' is one area undergoing significant changes - it will now be known as the Electrical Installation Condition Report with better recording of the tests carried out with a simplification of the codes indicating if the installation is dangerous or not.)