Or would I need to have done a level 3 btec specifically in IT because some universities all it says is a btec and DMM but doesn’t mention IT specifically.
Can I do a computer science degree with a btec level 3 in business? Or would I need to have done a level 3 btec specifically in IT because some universities all it says is a btec and DMM but doesn’t mention IT specifically.
Short answer: Yes you can, but your options will be more limited than if it was in IT/Computing.
As you've probably found, many do require that your BTEC Extended Diploma be in IT/Computing. For example Queen Mary (here) say "RQF Computing only" and Nottingham (here) say, "IT, IT (Business), IT (Software Development), IT (Networking and Systems), Computer Science and Networking and Computing/Computer Science".
At other times, they'll be more flexible with the BTEC but will require an A level along side it. For example Sheffield (here) say, "Engineering, Applied Science, IT or Computing + A in A Level Maths". Bristol (here) go even further in terms of flexibility (but still require an A level too) as they say, "Engineering BTEC National Level 3 Extended Diploma, plus A in Mathematics at A-level (or equivalent), OR any Applied General BTEC National Level 3 Extended Diploma,plus A in Mathematics at A-level (or equivalent)."
Others will not specify any particular BTEC subject requirement at all. For example, De Montfort (here) simply say, "BTEC National Diploma/ Extended Diploma at DMM". That flexibility in terms of subject is also reflected in their UCAS point-based offer ("A typical offer is 112 UCAS points from at least two A-levels or equivalent"). Similarly, Huddersfield (here) just need "DMM in BTEC Level 3 Extended Diploma" with no subjects specified. Again, this matches the way that handle A level and UCAS point-based requirements: "BBB at A Level, 120 UCAS tariff points from a combination of Level 3 qualifications."
Finally, there are some which specifically say Business is acceptable. For example, Plymouth (here) say, "DMM-DDM – science related subjects: IT, Humanities, Engineering, Software Development, IT Practitioners, Business, Computing, Science".
Universities don't have secret, unpublished, entry requirements. If they need a particular subject, they'll let you know. If they're happy to accept any BTEC Extended Diploma, then they simply won't specify that it needs to be in a particular subject. As you can see from the above, the fact that your BTEC is in Business will limit your options - but it won't prevent you meeting the entry requirements for Computer Science everywhere.
Or would I need to have done a level 3 btec specifically in IT because some universities all it says is a btec and DMM but doesn’t mention IT specifically.
Many especially top universities require A level Maths in addition to BTEC. Others accept with a set GCSE Maths grade. Only the individual university can tell you their entry standards,
Or would I need to have done a level 3 btec specifically in IT because some universities all it says is a btec and DMM but doesn’t mention IT specifically.
I am in the same postion and want to do Com Sci at Uni and I do BTEC Business Level 3. What Uni did you go for and which Unis gave you an offer. Thanks.