Since April 2009, landlords or agents should serve a letter before claim when planning court proceedings.
When to send letter
A section 8 notice is ideally served when a tenant is two months or more in arrears. However, a pre action letter could be sent earlier than this in order to save time.
Therefore, serve a pre action letter either when the tenant is at least one month in arrears, say, after two weeks arrears. Obviously, if you think they are likely to pay albeit late, there is no need for a letter. This should only be served when you think you might have to seek possession when they hit 2 months arrears.
If the tenant is already two months in arrears, it is best to get the section 8 notice served. However, you might be wise issuing the pre action letter the following day, so both letter and notice expire at roughly the same time, so as not to cause delays in commencing proceedings.
It is arguable that the section 8 notice alone will be sufficient without the need for an additional letter because the section 8 pretty much contains all the information needed in a letter. However, until this is formally decided, it is wise to also issue a letter.