It would be worth having a look at your council's GIS viewer for maps of the water network to see if that Toby is part of the mains network (council responsibility) or if that feeds a dwelling.

If anything, still report it and get it checked since water leaks is a nationwide problem. 

When you turn off the toby and the leak stops, does this confirm in your mind that the leak is on the house side of the toby?

A leak on the house side of the water meter (which is usually in the same place as the toby) is the responsibility of the homeowner to fix.  Calling a plumber is likely to be your best course of action.

I've had this happen around 10 years ago, and the unexpected bill was unwelcome but not too expensive as the leak was easy to locate and fix.

We're on a shared driveway and had a leak around the toby and appears on the house side of it, called the council anyway who came around, assessed it and fixed it themselves with no cost to us, seems if its on or close to the toby they'll sort it.

Odd as the council maintains up to the toby, shouldnt matter where its located. If you have water meters (or they are coming) then they'll work on it.

We're lucky I guess as our toby is on the shared driveway

Here in Whanganui they will only maintain if the Toby is on the street

If the Council have a map showing services you could find there is another toby at the end of the drive that is where the Council's responsibility ends.

I have heard that this is extremely dependant on exactly which council it is, who you talk to at said council, and what the policy is this week. Apparently they're not very consistent, and will often (but not always) approve good-will repairs. The exact legal point where it's the council's actual responsibility to repair the leak is apparently not exceptionally well defined. 

To answer your question it’s an easy fix….replace the tap in question, but where’s the water meter? (With the tap or is there only one meter for the 5 properties).

suggest you simply stump up for a plumber….they will be done quicker than you can say “what, $150 ish to do that”.

(ring a couple plumbers, it’s your best defence with overcoming any future issues (insurance etc).