Guidance for Candidates and Agents at UK Parliamentary general elections in Great Britain

The earliest you can officially become a candidate is on the date the UK Parliament is dissolved.

You will officially become a candidate on this day if, on or before this date, you have already declared yourself a candidate at the election (or another person has declared that you are a candidate).

If, after this date, you or others declare that you will be a candidate at the election, you will become a candidate on the date such a declaration is made, or on the date that you submit your nomination papers, whichever is earlier.

Once you have officially become a candidate, you are entitled to a copy of the electoral register.

You are also entitled to a copy of the lists of absent voters for the constituency you are standing in. 
In addition, you can use publicly funded rooms and schools for public meetings.