You are doing your MBBS in India, keen to pursue post graduation in England. You DO NOT NEED the GAMSAT, UKCAT or BMAT exams as all these are exams for starting the MBBS in England.
For postgraduation in the UK, the format is very well streamlined
1.Once you finish your MBBS from a recognised college in India (listed in the WHO registry of recognised medical colleges) you would start the program of FT , this is a TWO-year 'Foundation training' program that is similar to the house-surgeon or internship post of Indian training. Here you focus on the basics of clinical history, investigations, getting access, prescribing drugs etc.
2. After two years of FT comes the CT 'Core training' of two years. This post is like a Senior house officer or a non-PG resident job.
3.After CT comes the ST, this 6 years of 'Speciality training' enables you to become a consultant in the field of your choice.
4.For instance, after MBBS, if you intend to become a surgeon in England, you will do FT1, FT2, then CT1, CT2, then move on to ST1-6 and then take the final exit exams.
Please go through this link for surgical training (https://www.rcseng.ac.uk/careers-in-surgery/careers-support/entry-requirements-and-training/)
5. Since you have not mentioned your postgraduate choice, let's take some examples. Along with the training mentioned above, you will need to take the membership and the final Fellowship exams in the speciality of your choice.
MRCS and then FRCS for surgeons including orthopaedics.
Primary and final FRCA for anaesthetists.
MRCP and FRCP for internal medicine specialists.
6. Since you are an overseas candidate you will need PLAB (some specialities have an exemption) + IELTS, a GMC registration and meet the visa/work regulations to be employed as a doctor in training in the NHS England.
7. There is a program called as MTI - Medical training initiative which focusses on getting overseas doctors to have higher medical/surgical training in the UK. Many Royal colleges have this program (https://www.rcplondon.ac.uk/education-practice/advice/medical-training-initiative). This would be useful for you.
8. I would suggest try and meet consultants or medical college staff who have a UK qualification and interact with them. Also, browse through GMC website (https://www.gmc-uk.org/registration-and-licensing/join-the-register) and the royal college website of the speciality of your choice.
9. Try to have a presence in the academic section by presenting papers, undertaking short audits and studies while you do your internship under the guidance of your teachers. Keep a good logbook of what all you learn and do during intership, it will help you.