Higher compensation for delayed flat posession

1) you can move consumer forum and seek compensation st higher rate 

2) you can claim rentals paid by you for delay in delivery of possession 

3) you can also claim compensation for mental totrure undergone by you 

Dear Mr.Agarwal

1) Various consumer dispute Redressal agencies(National Commission, State Commission& District Forum)  have been awarding compensation to buyers for delayed possession of flats.

2) Any agreement where in the terms of contract are such that 
          a) The builder charges compound interest @ 18% per annum in the event of the delay on the part of  the  buyer in making payment to him  
                                                 and  
           b) the builder opting to pay Rs7per square feet per month for delayed possession of flat 
is wholly one sided, unfair and Unreasonable and hence it constitutes unfair trade practice within the meaning of Section 2(r) of the Consumer Protection Act, 1986.

3) Before approaching the court,we should also be conscious of the fact that the compensation is normally based on the following factors:

3A.) In disputes wherein the buyer wants to opt out of the contract and want a full refund of their money, the consumer courts normally grant a higher percentage of interest (18%)
                                                                          and 

3B) In disputes wherein the buyer wants the speedy completion of project and the possession of the property thereof, the courts issues  orders directing the builder for early  completion and possession of the property and in such cases depending on nature of agreement, may also order the builder to pay bank interest as prevalent on the date of contract. 
                                                          and
3c) In some cases depending on the nature of grievance, the courts also issue orders to the builder to reimburse the costs of alternative accommodation costs so incurred by the buyer.  

4) So in your case, since you have got possession, the consumer courts may be inclined to 
         4a)  Award a compensation equivalent to bank rate of interest that is being paid by a Nationalised bank on their 3 year Fixed deposit and 
          4b)  Courts may also issue orders Reimbursement of Alternative accommodation costs (subject to you providing receipts and payment details of the same).

Hope this helps.

You may first issue a legal demand notice to the builder demanding interest at a higher rate than mentioned in the BBA for delay in handing over possession of the flat mentioning all the aspects including the rent you had to pay for the interim period and the higher rate of interest you had paid for the loan amount for this purpose etc.
Let the builder give a reply denying the demand quoting the relevant clauses and express that he is not liable to pay anything beyond that. 
You may drag the builder to the consumer forum seeking not only higher or enhanced rate of interest for the delayed possession but also a handsome amount towards compensation for the mental pressures and agony you underwent due to this. 
In any case he cannot deny the agreed amount, in fact during the consumer case proceedings, he may come down with negotiation plans for an out of court settlement too which may be a win win case for you. 

Did you take possession under protest? Unless the answer to this question is in affirmative you cannot claim compensation?