I had a quick look at the guidelines for Common Assault, and they include, inter alia, the following:-
Factors indicating higher culpability: 1. Use of a weapon to frighten or harm the victim 2. Offence was planned or sustained 3. Head-butting, kicking, biting or attempted strangulation 4. Offence motivated by, or demonstrating, hostility to the victim on account of his or her sexual orientation or disability 5. Offence motivated by hostility towards a minority group, or a member or members of it 6. Abuse of a position of trust 7. Offence part of a group action
Factors indicating a more than usually serious degree of harm: 8. Injury 9. Victim is particularly vulnerable or providing a service to the public 10. Additional degradation of the victim 11. Offence committed in the presence of a child 12. Forced entry to the victim’s home 13. Offender prevented the victim from seeking or obtaining help 14. Previous violence or threats to same victim
Reports suggest that head-butting was indeed present, and it is, I imagine, arguable that point 5 might apply, since Conservatives have been a minority group for some time now. It is a little more questionable whether the MP victims were 'providing a service to the public'. You will have your own view about that. In the event of a conviction the court must consider compensation. Since the alleged assailant claimed two hundred thousand quid in expenses last year, he can probably afford to cough up. I can't see him passing the Legal Aid means test though.