Deed of variation- estate charge

[housemove21]

3 weeks until our mortgage offer expires and are meant to exchange on Monday.

we are selling our house and now our buyers solicitors are saying their lender need a deed of variation for the estate charge that states that they need 21 days prior notice.

We have a transfer deed that says this and states within it that before exercising any such powers and remedies the Rent Charge owner shall have given no less than 28 days prior written notice of its intention to do so to any mortgage lender.

Our solicitor has said  In their opinion they feel a Deed of Variation is not required as their lender required the notice period to be 21 days but the transfer deed as currently drawn provides for 28 days. 

we are waiting to see if this will be ok- surely it will as we have what they are asking for.

The lender is Barclays.

im just looking for advice or someone who has been through something similar.