I'm afraid that your only way into teaching in the UK is through a B.Ed. degree or a.n.other degree plus a P.G.C.E. from a British Teacher Training College or University (or the equivalent thereof.)
You could however, apply to become a Classroom Assistant in a school thus gaining experience of 'classroom life.'
Quite a few of the CAs that I employed went on to actually teach some lessons and, from there, went on to get their own degrees, eventually becoming fully qualified teachers.
Incidentally, apart from the Open University, you will find that most UK Universities demand two or three 'A Level' passes as entry qualifications.
If you are a 'mature student' however (25 or over) they will mostly only ask for one A Level pass in the subject of your chosen major.
I hope this information helps.
Please, anyone, correct me if I have given any erroneous information here - I have not been in the UK for over a year and legislation may have changed.
Al.
