Brighton:

• Preston park
• Royal Pavilion (visit for free some time in January)

London:

• afternoon tea somewhere in London
• deers in Richmond Park
• kew gardens
• see a musical
• shakespeare globe
• Tate Britain

Elsewhere in England:

• 2 castles
• 2 cathedrals
• 5 new cities (besides the ones mentioned in this list)
• Bath
• Stratford-Upon-Avon
• volunteer at a hostel somewhere up north