Can I complete Purchase While Title Plan is Updated?

Afternoon All.

I have a small problem with the purchase of a house and hope that maybe someone can give me a difinitive (legal) answer to.

The boundary as per the property title is incorrect and the neighbour is using a bit of the front of our property for his driveway and we are using a piece of his property for the back garden.

The vendor's solicitor has advised UKLR who have said that a "Land Swap" is required using forms TP1. The neighbour has agreed and it is all due to be signed and sent back to UKLR for correction.

Our mortgage offer expires in 5 weeks and due to personal circumstances we cannot extend. Our solicitor is demanding "Clear Title" (nothing outstanding at time of contract exchange) and so all this boundary stuff needs to be done before that time.

I have read that once the forms are registered with UKLR, the completion can proceed as both buyer and seller are protected whilst the forms are processed (somewhat like a registration gap).

Can someone tell me what is LEGALLY required from this mess to enable completion and is my solicitor being overly zealous?

Many thanks in advance

Simon - what they have advised re the land swap is what's legally required to transfer ownership.
What's required by a solicitor or perhaps your mortgage lender is more about 'risk' assessment than the legalities as how and when you exchange/complete is a conveyancing/lending decision so not a 'legal' issue. 
So if they need a 'clear title' before they will complete then the application(s) to register the swap need to be submitted. They then have to request expedition to keep the wait time as short as possible. Everything then hinges on the applications being in order of course.

There's no government UKLR and that relates to a third party service provider. If the land/property is in England or Wales then you would be dealing with us at HM Land Registry
And there's no 'All' on the forum as whilst others can comment they very rarely do as we use it very much for HMLR to answer enquiries only

Hi Adam, 
Thanks for your quick and full reply. 

Good to clear up my misconception regarding HMLR and UKLR 👍. 

Just a follow up if I may. 

As my time constraints are tight due to the mortgage offer expiring, do we need to wait for everything (new boundary) to come back from HMLR to declare "clear title" or is it accepted that as the TP1s are with HMLR that it will be completed and that would enable us to complete the purchase to the satisfaction of the solicitor / lender? 

Once again, many thanks. 

Hi Simon - that's the key Q for your conveyancer/lender to decide on.
A 'clear title' means that there is nothing pending against it when you want to complete. Whilst it is possible to complete knowing what's still pending with us, some conveyancers/lenders may not be prepared to but that's for their reason(s) so only then can answer/explain 
So it;s not a 'Can we?' question but a 'Will we?' one and if we won;t then why won't we and that's the answer you are searching for