I would go to your personnel/ HR person and request a 121 meeting to discuss the contract in further detail.
Explain that the contract differs to your current one, namely the specific reference to working pattern. Ask her why there is a need for a new contract? Why was a discussion or communication not made about the contract, instead of it just being "handed out" and requested to be sent back ASAP? Have all employees received a new one, or just you, or just part time people? If part time only people, request information on why full time people have been missed? Ask her what are the main differences in the contract and what that means for you?
Explain, politely that you are not signing the contract until you receive some answers about the above.
As for your sick pay, redundancy package etc, this should be detailed in your contract OR in the Company policy. Check for any discrepancies from old one to the new one. If there are some, effectively they are varying your contract of employment and should be consulting with you about the need for the changes. If the change needs to happen, they either get your buy in to change it, or give you statutory notice of the change (normally a month/4weeks).
As for your passport, she is checking eligibility to work in the UK. If you hold an EU passport, this is evidence of your nationality/status to work. I've never known organisations to ask for a new copy when a British passport has expired (normally only when visas expire). I would request her reasons for this in writing and also seek out what alternatives can be provided (such as birth certificate, P60 etc) if you haven't got an up to date passport.
Seems a little strange what they are doing but it could be a case of poor communication, hence my advice to go straight to HR person.
The flexibility clause about "reasonable notice" is pretty standard I'm afraid and even if you weren't happy with it, they would probably find a business need/case to push it on you, and terminate your old contract, rehiring you on this new one. Depends how much of a fuss you want to make and if it will even have that much of an affect on you; ie you work Mondays and Tuesdays, but they give you reasonable notice to work Wednesdays and Thursdays. Throw in dependents such as children and they will need to dread very carefully if changing your working pattern.