[SMHarman]

It's a reasonable request of an employer for you to work the hours of the client you are visiting, this will often be included in your contract, it can look pretty shoddy at the customer end if you are working 10:30 -3 because of travel time, the perception is that the firm is a bunch of slackers (note: perception)

The policy I have seen before for similar situations (in accounting, auditing at clients premises) was that if the journey to the clients took more than 30 minutes more than your usual journey then overtime (or TOIL) was payable. e.g it usually takes you 45 mins from leaving your house to being at your desk at your usual place of work, to leave your house and be at the client 60 mins later - no overtime, 80 minutes later 60 mins overtime paid.

Long Haul as a more junior person I was awarded travel days, one day each way if the journey was over 5 and under 12 hours, 2 days if over 12 hours. These were meant to be used as aclimatisation / jetlag days, e.g flying to Oz to start work on Monday, then leave on Thursday morning (travel day one) Friday PM arrive TD 2, the weekend and be refreshed to start work on Monday. Similarly on the return it meant you could catch up with bills, laundry etc, not be expected back at your desk the minute you touched down.

Nowdays we as a rule split the difference, especially on something like the London Scotland in the example. Leave early enough to be in the office by 10am on Monday and leave at about 3:30 on Friday so you're home at a reasonable time.

The law though, I would think most would be subject to the 45 hr working time reg as a restriction on travel, after all it is included in working time as it is wholly, exclusivly and necessarily for your employer. Looks like they are trying to increase the level of unpaid overtime they are getting out of you all.