There is currenlty a serious backlog, be prepared to wait one to two years to get the certificate from Land Registry after the purchse completion.
My experience is most of the tme, commnication with the law firm was by email, but I did made an appointment with the paralegal for sending to her the signed Contract of Exchange and other documents in person. It was the only visit to the law firm in the oveall process which took 5 months.