TennetClean
Let me enlighten you!
First off, do you know how to report the breaches of H&S! probably not! if you wont to know then I am full aware of this, and secondly you wont put them out of business because that is not what happens with H&SE they will be given a Improvement notice, then a Prohibition notice if they don't do anything, then and only then they will be Prosecution which takes a long time & many years, as that is the legal process in this country and there can be appeals
Now regarding the use of ladders for window cleaning is illegal! :

WAHR was written into UK law in April 2005, at the time one WFP surliper put pressure on the powers that be, to make the use of ladders illegal! they was saying the same as you ( Every employer shall ensure that work is not carried out at height where it is reasonably practicable to carry out the work safely otherwise than at height.")
And yes they do have a good point, however that agreement at the time was lost and they have moved on to tank safety!
You must remember that WAHR is a regulation and its down to each industry to implement to there working practices, this is where Fed of Window Cleaners & APWC come in! at the moment the guidelines for safe use of ladders in window cleaning
www.hse.gov.uk/pubns/misc613.pdf are under review, once they are completed, and every window cleaner complies to this guidelines then you are complying to WAHR
When I was on APWC I asked are H&S officer for are committee to help with compiling theses guidelines, having been a window cleaner for over 20 years and 15 years up a ladder, I think I have a very good understanding of whats needed, I have sat on my desk top, a file of the draft copy of the guidelines, and
its not illlegal to use a ladder for window cleaning I really do hope you can take this good advice and not waste your time and others!