Interesting CAA Safety Leaflet I was reading on britflight;
http://www.britflight.com/wingfiles/...iplinegood.pdf
Especially relevant to this thread are the required elements for initial call and frequency handover on pages 2 and 3;
Call on Departure
When flying Instrument Departures (including those outside controlled airspace) you must include the following information on initial contact with the first en-route ATS Unit:
• Callsign;
• Standard Instrument Departure (SID) or Standard Departure Route Designator (where appropriate);
• Current or passing level;
• Initial climb level (i.e. the first level at which you will level off unless otherwise cleared. For example, on a SID that involves a stepped climb profile, the initial climb level will be the first level specified in the profile).
The inclusion of the current or passing level enables the air traffic controller to verify the accuracy of the Mode C readout. Equally important is the inclusion of the initial climb level. This confirms that your understanding of your cleared level is the same as the air traffic controller’s. This confirmation reduces the chance of a level bust or, at worst, a mid-air collision.
Subsequent Frequency Changes
When changing frequency, unless otherwise instructed, the initial call must include aircraft identification and level information only.
Level information must be included in the report as follows:
• If you are in level flight but cleared to another level, the call must include the current level and the cleared level;
• If you are climbing or descending, the call must include the cleared level only;
• If you have been assigned a speed or a heading, this information must also be included in the initial call on the new frequency.
Why is this?
By sticking to this format a mutual understanding is confirmed between you and the air traffic controller, and a minimum of time is used to pass on the information, thus reducing RTF congestion. Mode C confirmation is not required in this case because it has already been verified on departure.
PP