Oldham is around the 700' amsl mark so I can only assume the controller was basing terrain awareness and the ATC clearance on that. The controller has no remit to tell you what to do outside CAS, and as no clearance can be given, then their responsibility can't start until the boundary. The clearance will be 'safe' from that point onwards, all things considered.
If you can't make the clearance because of other factors which are your responsibility to take account of, then shout up and advise ATC that you won't be able to make the restriction due to terrain, cloud, or whatever. As you found, an alternative clearance can usually be given.
It's not a criticism of Jump Complete since he/she has done exactly as they should have and spoken up to ATC but maybe it's a sign of our increasingly litigious society and the 'nanny state' that a section of society always seems to be looking for others to get them out of trouble and not take responsibility for their own actions and laid down responsibilities. What would cause a pilot to blindly follow an ATC instruction which does not apply to their current location, which would take them in to terrain which they can possibly see, or in to bad weather and cumulo granite when they know they are not qualified to do so. Is it this ? Because 'ATC told me to'. Is it poor training received or poor knowledge retention of self preservation strategies on some pilot's parts ? Or do some just prove Darwins theory ? I wish I knew !!
It's been mentioned in other threads on PPRuNe that access to CAS should be given more to pilots, particularly in busy airspace (e.g Heathrow area). One of the planks of this argument is that ATC should trust pilots, accept that they can aviate, navigate, and communicate competently. They are licenced after all. Yet here we see an inference that sometimes we maybe can't trust pilots to do the right thing. To fly beyond their capabilities and get themselves in trouble just because we give them a clearance which is safe inside CAS but they somehow can't think for themselves about how they are going to get to that point safely and won't adjust their flight path or ask for an alternative to ensure they don't become another statistic.
As Devils Advocate ... I don't think pilots can have it both ways as a general principle (as an ATCO, dealing with emergencies and duty of care if ATC notice any pilot errors would override any principle always) . It's either a mutual trust and an acceptance that the pilot has serious responsibilities they can cope with which ATC let them get on with. Or it's a 'nanny state' hand holding all the way with the pilot making sure that ATC are happy that he even breathes. As a pilot and an ATCO, I know which I think it should be.
Food for thought and an interesting topic. Thanks Jump Complete