1. Marriage performed before the registrar is popularly called 'court marriage' in common parlance. Registered/Court marriage as you call it is solemnized under the Special Marriage Act, 1954. All such marriages can take place between any two Indian citizens as well one Indian citizen with a foreigner irrespective of their religion, caste or creed, and you can say this is the secular form of marriage available in our country.
2. Such a marriage is solemnized before the marriage officer/registrar usually D.C. deputy commissioner of the area /SDM where both or any of the parties to such a marriage reside permanently or for at least one month. Cost of such a marriage is the rate prevalent in your area.
3. Now how you proceed? Both the parties to the marriage have to file a joint application before the marriage officer along with individual affidavit attested by notary public specifying the age, place of residence, marital status(unmarried or divorcee as the case maybe) mental status(not idiot or not with unfit mind), etc. Along with this you have to give proof of age (School certificate, Passport, Pan card), proof of residence (Passport, ration card, voters ID card, rent agreement), & the application/notice of such a marriage maybe asked to be witnessed by 3 independent adult persons, affix one photograph of each of the parties & all the 3 witnesses.
4. On receiving such an application/notice the marriage officer issues a month notice regarding the intended marriage & get such a notice affixed on the notice board out side his office, a copy of such notice is sent to the marriage officer under whose jurisdiction the other party lives, also a copy is to the individual parties address. After expiry of the period of notice a date is fixed on which all the persons parties to the marriage & 3 witnesses appear again before the marriage officer who declare them married & issue a certificate to this regard.
5. If the above procedure has been complied with threadbare then the earlier marriage of your wife is legally valid. A search would have to be undertaken by you at the office of marriage registrar to ascertain whether your wife had married or not.
6. A case for cheating and fraud can be filed against her if she did not disclose at the time of her marriage to you her earlier marriage.
7. Annulment cannot be filed now as it ought to have been filed within a year. You are well past that time limit.
8. You may file for divorce on the basis of desertion as your wife did not join you in London.