Any conveyancer accepting electronic signatures?

It's not the conveyancer you have to satisfy, but the law. Perhaps that's the reason they won't accept electronic signatures. Fraud is fraud whether it's the 21st century or not. Not that I am suggesting your transaction is fraudulent, but the risk is there, as electronic signatures can easily be faked.

I'm not a conveyancer but would a scanned signature suffice?

Since 18th April 2017 Digital signatures have been used in the exchange of contracts for a residential property transaction in England. As most solicitors still like to work the old fashioned way, even if they allow digital signatures, you often find they resort to wanting a wet signature on hard copy contracts. I can introduce you to a firm (no fee if no completion that subscribes to DigitalMove (DigitalMove allows clients to digitally sign documents on their desktop, tablet, or smartphone device from the comfort of their own home, 24/7) but before I do I suggest you call the eConveyancing platform provider to first check; 01844 262397. If they confirm what I say & you do want to use them, ask if you can deal direct or if you have to go through an approved Broker whereby email me at laura.stonard@openwork.uk.com & I'll tell you what info I need to get you a quote which if you're happy with, I can instruct on your behalf & back out gracefully. Alternatively use the likes of FedEx who are extremely efficient.

one accepted a signed document sent by fax.

It's not as simple. It's a high-value transaction, so a mistake (surprisingly often) in the transaction is usually expensive, and the solicitor is accountable financially to the parties and professionally to the SRA. Also, as Smartermind highlights, we're all caught by the anti-money laundering measures.
Timing is also against you. With earlier sales delayed, paper-based processes are slower for home-working, plus the Stamp Duty reduction, good conveyancers don't need to look for work.
Whilst that's all negative, I have forwarded it to my son who works in conveyancing for suggestions.

https://hmlandregistry.blog.gov.uk/2020/07/09/electronic-signatures-in-conveyancing/

If Land Registry can accept them...

E-signatures are now widely used and legally acceptable for high value transactions. Given the backlog, I would have thought conveyancers would be desperate to use anything which eases the load. Docusign offer a free solution if all you need is to sign documents on an ad-hoc basis https://go.docusign.co.uk/o/free/?tgr=com-freeplan-Pricing?tgr=com-freeplan-Pricing&_ga=2.46198567.1041520026.1604576167-51066863.1602849605&_gac=1.245689904.1602849605.EAIaIQobChMItPCKqIO57AIVw3_TCh111w5aEAEYASAAEgJwI_D_BwE

My letting agent uses DocuSign which is legally valid I believe

Richard Spencer > https://www.converselaw.com/team/richard-spencer

Hi Heather,
I have suffered the same issues as I live in South Africa 4 weeks to get post sounds good to me, try 4 months or not at all. I now get documents sent DHL go to a commissioner of oaths ( a south african solicitor who is also a registered as a commissioner of oaths) Produce passport and complete paperwork in front of him sometimes need a witness also. Once done return paperwork DHL around 10 days in all. It's a small price to pay depending on urgency and value of transaction. I hope that helps.
Regards
Chris Bunn

I am also a South African BTL investor. The property we completed on last year only required an original signature on the final sales agreement. Our solicitor emailed us the document which we printed, hand signed and then couriered to London via an overnight service. The exercise took 2 days.