Sounds like a letter from Dept of Work & Pensions (DWP) (there is no Department of Benefits, although there is a Benefits Agency(BA)) regarding a wage replacement benefit based on ill health / disability - either Incapacity Benefit or Employment & Support Allowance (ESA).
Many people are finding that recent medicals are leading to loss of benefits. The advice is always to seek advice from a benefits advisor eg CAB (Citizens Advice Bureau), local council service, disability rights body etc. Success rate at appeal tribunals is higher if you attend in person than if you ask for a hearing on the papers, and higher if you are represented by an advisor, although some don't attend any tribunals, but taking a written submission can help.
In addition, worth mentioning that if you are also on Disability Living Allowance (DLA), DWP may use the medical examination to look at your DLA award as well.