Property purchase - seller's solicitor failing to certify freehold transfer e-signaure

I purchased a freehold property last year for which the sellers have signed the freehold transfer and their solicitor has provided it to my solicitors who then submitted the application to the Land Registry to register the change of ownership.
 
The problem is that the sellers signed the transfer electronically and in order for the Land Registry to accept this a certificate from the sellers’ solicitor is required, confirming that this was done in line with the Land Registry’s requirements. As of yet they have failed to provide this meaning that the transfer has not been completed. 

We are now looking to place this property on the market and despite attempts to motivate the seller's solicitor to provide this certificate they have failed to do so. My questions are: a) does this present a barrier to the sale of the property and b) is there any way that this issue can be flagged by the Land Registry directly to encourage the solicitor to resolve the issue?

Thanks in advance for any advice or guidance!

Nathan - sorry to read of the issues you are facing
a) invariably yes but very much a Q for your conveyancer/the buyer to answer for you
b) no, your conveyancer will have obtained an undertaking from the seller's conveyancer to assist/deal with such matters - they need to enforce the undertaking 

Hi Adam

Thanks for the quick reply confirming the suspicion the ball is thoroughly in the court of the seller's solicitor. In order that I can make this as straightforward as possible for them are there any resources or materials available which can explain what's required and how best to provide it? Anything that can break this deadlock would be a great help. Thanks

Nathan - I'm sure they are already aware but our PG on the subject may be of assistance - Electronic signatures accepted by HM Land Registry (PG82) - GOV.UK