Yes, you can apply online and fixed date for registration of your marriage certificate on that day you both has to be present.

In my opinion, get the marriage certificate from UK and apostilled in UK so that the same can be applicable in India or vice versa.

1) you must have been married under provisions of special marriage act 

2) for marriage between Indian and foreigner it has to be done under provisions of special marriage act 

3) 

ffidavit by both the parties stating place and date of marriage, date of birth, marital status at the time of marriage and nationality and that the parties are not related to each other within the prohibited degree of relationship as per Special Marriage Act

4)?Two passport size photographs of both the parties and one marriage photograph

1. It is not clear whether you married as per Hindu rites and customs only or got your marriage registered as well.

f your marriage was registered under Hindu of Special Marriage and if the certificate is lost then you can apply for its certified copy.

Otherwise you will have to apply for registration of your marriage under Hindu Marriage Act afresh

For Marriage Registration under Hindu Act: You can apply at office of the Sub-Divisional Magistrate in whose jurisdiction the husband or wife resides. 

Memorandum of marriage has to be filed and submitted before the registrar to get the marriage certificate. 

An application has to be made before the registrar at the jurisdictional area,

If you have married and the same is not registered in India you will not get the same.  Now you have to again register the same. You need to go give poa to someone attested at embassy or high commission who will proceed and file your info in India for registration

As you are already married and have sufficient proof of marriage then you can apply for marriage certificate in India on the basis of the memorandum available with you the marriage registrar will take 30 days to issue a marriage certificate and for this purpose at least one has to come back to India to follow up the procedure it is not very difficult and you will get that

You may have to apply for registration of your marriage under the provisions of Special marriage act in the jurisdiction where your marriage was solemnized. 

You may have to follow the procedure as laid down in law for this purpose. 

You both may have to fly to India for this purpose as the registrar may require you both to be present for signing the register held in his office for registering the marriage and to issue the marriage certificate. 

1. Actually you two should have registered your marriage in India before the Registrar of Marriage.

2. What is that Memorandum of Marriage? Who had issue it?

3. You now shall have to get your marriage registered before the Court by filing an application or  get your affidavit of marriage affirmed before a fist class judicial Magistrate with a directive to accept the said affidavit as certificate of marriage.

Was it a court marriage ? AS marriage with non Indian can solemnized under special marriage act, court marriage. Municipality has no jurisdiction to issue marriage certificate for non Indian even if marriage held by performing rituals.

Try to apply at Embassy but rare possibility to issue back date certificate.