One of the more famous tours is run by the Canal Museum:
Summer Canal Boat Tours
Travel by boat through Islington tunnel on the Regent's Canal, opened
in 1820, and around three quarters of a mile in length. When it first
opened boats had to be pushed through by a process of "legging" where
men lay on the boat and pushed against the walls with their legs. Our
trips are more easily achieved on board one of London's community
narrowboats. We use the historic converted working narrowboat
Tarporley, for many of these boat trips. A guide from the museum
offers you a commentary on the history of the tunnel as you cruise
through it.
Prices and dates
Prices are £8.30 adult, £6.00 children, including admission to the
museum. The boat trip is not offered on its own without museum
admission. Please visit the museum before the boat departs if
travelling on the 1500 or 1600 trips.
Dates for 2014 are the second and fourth Sundays of May to September,
and 2nd Sunday of October.
May 11th and 25th
June 8th and 22nd
July 13th and 27th
August 10th and 24th
September 14th and 28th
October 12th
Departure times from the museum:
1100
1200
1400
1500
1600 (no re-entry to museum after this trip, which will return to York Way, close to King's Cross station, or to the museum without
access to the building)
More information is available on their website, and I assure you if you want a tour longer than the hour or so they offer, they'll be able to point you in the direction of other companies. Similarly, if you wanted to hire one yourself for a couple of days.