The problem with this situation is there is a MASSIVE grey area and is open to too much interpretation,
example, you can take your car for a mot and it could fail on a major defect then if you drive it home and the police or vosa see that it definatly has a major defect then you could get done for using it in a dangerous condition. However the law says you can drive "to and from the place of repair" no mention of condition once checked, as in minor defects can be driven away and major defects need to be repaired on site or trailed or even how many miles away your allowed to travel ect ect ect

In the real world it would depend on circumstance and the person you deal with.
If you get a jobs worth and your going long distance in a death trap and tell him you getting it repaired dont be surprised if you end up in trouble.
But if its pre booked and down the road i doubt you would have any trouble.