At £6 an hour, your friends would have only been 7p per hour over the minimum wage!!!
Even if they worked an 8 hour day and 7 days a week for 52 weeks of the year (no time off at all!), they would only be earning £203.84 over the minimum wage for the whole year.
From this you would have to take off tax and national insurance, business insurance, fuel to travel to jobs (assuming you don't walk everywhere carring your kit with you of course), vehicle insurance (including business use of course), vehicle tax, maintenance etc. Not to mention accountancy fees and all the associated costs of payroll etc.
Unless your friends who were charging £6 an hour were able to do all of the above for under £208.84 then the were in fact working for less than minimum wage!
Could it be that they were not insured to be doing that work and were therefore putting their customers property at risk?
The 'Polish Revolution' is a phrase that has been used to describe the illegal running of businesses using exploited Polish workers who receive lower than minimum wage to do work in the UK, usually uninsured, unqualified and untrained. The result of such practice is the lowering of prices to a point where properly run businesses find it difficult to compete on price alone.
If you are running a legitimate business and complying with all the rules associated with such an activity then there is no reason for you to be offended by this phrase, however if you are in fact running an illegal, exploitative and immoral business as described above then please feel free to be as offended as you like.