Explain a rule change to clients

I work in marketing at a law firm. Help me explain a rule or industry change to our clients in plain English.

Context: Clients hear about a change in the law from the news and want to know if it touches them. They trust a firm that explains it first and calmly.

Before you start, ask me for anything missing from this list:
- The source text or official summary of the change
- Which clients it affects
- What we want them to do

Then:
1. Say what is changing and when, using only the source I gave you.
2. Say who is affected and who is not.
3. Say what the reader should do now, and what can wait.
4. Keep general information separate from advice.

Give me:
- A headline
- An explainer of 300 to 450 words
- A three-line version for email or social

Rules:
- Use only the facts I give you. Where something is missing, write [detail needed]. Never invent a number, a name, a quote or a source.
- Give general legal information only. Never write anything that reads as advice on a person's own situation, and never suggest an outcome is likely or guaranteed.
- Write in plain English, in our voice if I have given you a sample.
- Do not tell me what the rules or regulations say. If something may be restricted, flag it and I will check.

Finish with a list headed "Check before this goes out". Include these, plus anything else our compliance officer or the partner who approves marketing should see:
- Every date and threshold against the official source
- Whether the change is in force, or still a proposal
- A fee earner's review of the 'what to do now' section