Depends on course. They have always been pretty much essential in my studies as lectures are simply not in depth enough.
I have come across many students who do not buy textbooks and I think thats pretty insane. You should have the main one and not buying it is false economy imo.
Should you have the latest edition? It depends and that can be subject specific as well. Some subjects it is important because the course depends on knowing the latest developments. Its false economy again or extra hassle knowing your copy is x years out of date.
2nd hand and buying a copy with someone else or within a group can work.
Considering you are going to get into debt by £40,000-£50,000, then I think trying to save a few £ by not buying books is stupid. I see them as investment. If you wnat to recoup the money just sell them the following year for half price. I would wait a few weeks or talk to a few srudents in the year above and they cna give you an idea what was important.