in layman's language:-

the fact that an employee claims and receives sick pay after walking out of his job in response to seriously wrong treatment by his employer does not of itself prevent the employee claiming unfair constructive dismissal .

in legal language:-

claiming and receiving sick pay in those circumstances does not necessarilly mean that the employee has affirmed his contract.

For relevant general notes see Constructive dismissal/a general note and/or Whistleblowing/a general note .