Does the client need to print the contract, physically sign then scan and return a digital copy?
In the UK, no, they do not need to. However it is regarded as good practice to do so. Especially if the project is anything greater than a simple or small task for a small amount of money.
Is a simple email reply to the sending of the contract saying "I agree, please proceed" enough for the contract to be assumed agreed on?
EDIT *** No, not quite. **** REMOVED
Normally, yes. You need four elements.
An intention to enter into legal agreement (We intend for you to do this work)
An offer (we will do this for you by this date or from this date.)
A consideration to enter into legal agreement (We will pay this much)
An acceptance of the offer (the 'Yes go ahead', not a continued discussion)
What I do is to create a document 'Outline/Schedule of work' (versioned) describing what we are going to do. A separate document 'Quotation' stating for work as described in the Schedule of Work, including a schedule of payments: ie 30% deposit, 30% on this date, 40% on completion.
I then, in those documents, refer to a third document as 'Subject to our standard Terms and Conditions of service' which is a one page, simple plain english document, available publicaly on our website, saying we will do whatever we can to achieve the goals. The client will provide required materials in a timely basis. Payments are non refundable. All work product belongs to client upon completion of the project. Everything is private and sharing of information with third parties can only be done with the consent of us and the client. Additional work not included on the work schedule will be charged seperately. Quotations are valid for 3 months.
The key here is payments are non refundable.
I then say that if they want to go ahead as soon as we get the deposit we will begin work as laid out in the scheme of work and subject to our standard terms and conditions.
That is it, they do not need to email me to say 'Yes please, go ahead', scan or sign anything or whatever. The payment is a clear indication that they accept our terms of service and the schedule of work, without any fuss, and have entered into an agreement.
I had one customer say 'we want a refund' when an addition to their schedule of work they deemed too expensive. I pointed out the terms and conditions (which incidentally should be versioned and dated) and they quietly backed off.
The emails sending the quotation and schedule of work I keep safely stored away for reference as well as in all honesty all communications. If they want to make a change to the schedule, the quotation and schedules are both updated and sent again. "Please find the ammended schedule of work and quotation V1.02 dated 12th May 2016 replacing any previous documents." There can be no confusion then over what schedule or payments are required.
The key is to be clear, upfront, with everything clearly documented preferably in an attachment, with a reference number and date on every document sent.
Hope that helps,