Hi Matt,
I finished a day release construction-related degree (not Civil Engineering though) in the early nineties which lead to a "Chartered" qualification.
In the early noughties I sold my practice and did the ATPL written exams as part of a modular training scheme.
The biggest difference you will notice is that for your degree you were writing, reasoning and arguing with a tangible person (be it Tutor, Study partner, Assessor, etc etc) and where ultimately you were probably not judged on whether you were right or wrong so much as the persuasiveness of your argument and the clarity of your ideas and presentation.
Well you can forget all that, you will either be Right or Wrong for the purposes of the ATPL (with certain limited grounds of appeal), you are not trying to convince or reason with anyone except a computer checking your mark-sheet and nobody is interested in your intellect at the end of the day, only your ability as Ghengis says to memorise facts and (sadly in my opinion) question banks. Plus you are working against the clock.
Of course intellect comes into it during the learning process because if you can grasp basic principles you should be some way towards being able to answer any question thrown at you without needing to have seen it before. Unfortunately it tends not to work that way in practice, because the volume of study material is undeniably large, and the training organisations will tell you which bits you need to know, which you can forget, and what questions may crop up for each area.
Thus people with minimal knowledge, but an ability to memorise feedback questions and answers, can theoretically pass all 14 exams without really ever learning very much.
In this respect, do not let anybody try to persuade you that the ATPL exams are in any way an equivalent academic qualification to a degree (as some have tried to do on Pprune in the past), there is no comparison whatsoever.
As to the practicalities, well my degree was 5 years with Day release and working evenings and one day at the weekend at the books. For the ATPLs I chose the "total immersion" method, going to a full time ground school for 6 months and completing all 14 in that period. It was hard work I will not deny, and I basically cut myself off during that period, but it was do-able and I managed first time passes even though I am no Brain of Britain.
However there were kids (yes kids) in the class who clearly thought they were just there to mess around, probably thought they were already great pilots too, and they put in little or no work thinking it would all be handed to them on a plate, and failed spectacularly (yes, even VFR Comms).
To have finished a degree demonstrates that you have commitment, and this you will need for the ATPLs. However if you are able to cope with construction centred calculations there is nothing mathematical in the ATPLs which will give you trouble. If you have understood the physics of construction there is similarly little or no mystery to the physics involved in ATPL Principles of Flight.
However the pass marks are high (75%) so perhaps a little higher than required for a 2:1 degree but less than a First.
You may need to adjust your learning methods somewhat but you should not be daunted by it. As to whether you go "Full time" or Distance learning, I think that depends on how well you work at home, and how long you want the process to take.
Hope this helps a little.
SJ