Is this Legal?

[Iggypoppin']

I'm going to pose this Hypothetically, so as not to get anyone in trouble.

Suppose, Hypothetically, there is a large group of mates. all range from around 16-27 and love cars. They have, slowly and without really noticing, come to hang out at the eldest car enthusiests home, who has no objection, and who's wife and kids love it too. there is about 10-20 of them, not all there at the same time, about 7 or 8 are always there after 5. they repair each others cars, project cars and focus a lot on the eldest guys project, which, for this argument, is say, a KE70 corolla fitted with an RB26 and is a proper ground up rebuild not a junk pile ie: 10's of thousands gone in. the boys all meet up after work, do some work maybe a little swearing, plenty of cars, sometimes as many as 20. they keep as quiet as a mob of guys can. when they leave/arrive they are civil and dont hoon off and leave skid marks everywhere. one day the police arrive at the door and warn the renter of the household (our eldest@ 27 yrs) that he is to cease all power tools noise, no cars, no working on them, after 5pm as he is suspected of running an illegal chop shop(note: other boys cars coming and going etc. NO MONEY CHANGES HANDS) fair enough power tools at 9.30 at night is excessive but that is a rarity and its all pretty much over by around 10 anyway. My question is, can the police actually enforce this kind of order? nothing in paper but apparently they have "evidence" to suggest otherwise and when they are asked this, they say, "most backyard mechanics only have socket sets and maybe a grinder no welders and pipe benders". It is confusing that they know whats in a locked and unwindowed shed....isnt it?