Gypsies and travellers have begun trading horses at this year's fair.
Thousands of members of the travelling community have arrived from all over Europe to take part in the annual tradition.
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The 12.5 hour walkout by 63 GMB members got under way at 6am this morning and will continue until 6.30pm this evening.
37-year-old Graeme Haddon pleaded guilty to the offence which happened in his home village of Lamancha near West Linton at the weekend.
Laura Price was dragged into an alleyway, close to Penrith Leisure Centre, where she had her head jumped on and kicked "like a football".