A law firm sends you a letter of demand when they have not attempted
to contact you before that.
A letter of demand is the usual first contact. What else would the law firm be writing to you about other than to demand that you pay what you owe their client?
Is there a legal procedure in debt collection?
In england-and-wales, the majority of debt claims end up in the County Court which is governed by the Civil Procedure Rules. Before bringing a claim, the parties are expected to follow the Practice Direction – Pre-action Conduct and Protocols.
If there is a specific protocol, then you follow that; otherwise you follow the general one in the above link, pursuant to Para. 1(2). A list of specific protocols can be found at Para. 18 but note that this is slightly inaccurate and you should also check the list here. If the debt is being pursued by a business against an individual then the Pre-Action Protocol for Debt Claims applies. I won't go into detail on the procedures themselves since you can read them directly in the links I've provided, other than to say that they do contain provisions relating to what information should be communicated between the parties prior to initiating proceedings. For example, under Para. 6 of the general protocol:
The steps will usually include—
(a) the claimant writing to the defendant with concise details of the
claim. The letter should include the basis on which the claim is made,
a summary of the facts, what the claimant wants from the defendant,
and if money, how the amount is calculated;
If a party fails to comply with the applicable pre-action protocol, this does not affect the outcome of the case (i.e. whether they win and if so, what they are awarded). Instead, it gives the Court discretion to apply sanctions in relation to costs and interest. Under Para. 16 of the general protocol:
The court will consider the effect of any non-compliance when deciding
whether to impose any sanctions which may include—
(a) an order that the party at fault pays the costs of the
proceedings, or part of the costs of the other party or parties;
(b) an order that the party at fault pay those costs on an indemnity
(c) if the party at fault is a claimant who has been awarded a sum of
money, an order depriving that party of interest on that sum for a
specified period, and/or awarding interest at a lower rate than would
otherwise have been awarded;
(d) if the party at fault is a defendant, and the claimant has been
awarded a sum of money, an order awarding interest on that sum for a
specified period at a higher rate, (not exceeding 10% above base
rate), than the rate which would otherwise have been awarded.