Can Severe Disability Premium be backdated?

Hi,

I applied for ESA approximately 3 months ago and am still in the assessment phase waiting to hear about the physical assessment.

I applied for DLA and was denied it and so appealed.....they overturned their decision on appeal and awarded me high rate mobility and low rate care.

I have now been advised that I can apply for SDP and was wondering if it is granted will they back date it and how far??

thanks
Emma