"The computer equipment has been seized but no arrests have been made, the force said."
Whoever does get arrested for this, they won't be facing the same charges for intent to supply drugs. I'm not sure on the penalty of stealing electricity, but it's probably a lot less severe.
In a consumer setting, I would be also be surprised. In this setting where it probably isn't clear exactly who the perpetrators are, you seize the assets until you can figure that out. I'm sure this wasn't all being done by "Sandwell Bitcoin Miners Ltd.", a registered British corporation majority owned by Joe Sandwell.
Here in the UK we have what's known as CPSPOC, or "Criminal Prosecution Service Proceeds of Crime" unit. Their job is to recover all proceeds from criminal activity. In this case I imagine they'll try to argue that the bitcoins mined with stolen electricity are proceeds of crime, and they'll confiscate them. The money recovered will go to the treasury after the electricity company has been compensated.
That assumes they can actually get the Bitcoin. It's also likely that there won't be anything left after compensating the power company, since the mining operation was likely unprofitable if taking the cost of electricity into account.
If they can't then they can also charge the people behind the electricity theft with a bunch of additional crimes about withholding the proceeds of crime, money laundering, refusing to hand over encryption keys, etc. If the operation was unprofitable that doesn't matter either - if the CPS determine you mined, say, 1000BTC then that's what you 'owe'. If you can't pay it then they'll seize your other assets up to that amount. That money is then used to pay the electricity company, government, etc.
The law is very much rigged against you if you're caught.
It might have been profitable 2 months, it's not anymore and soon it will seem silly (when BTC drops below 20k) even until the next bull market comes along.
Whoever does get arrested for this, they won't be facing the same charges for intent to supply drugs. I'm not sure on the penalty of stealing electricity, but it's probably a lot less severe.