My wife whilst at work was using a knife to cut a hard substance, (rose wax) in the cosmetic industry, this was a tool supplied by the employer.  The knife slipped causing a small cut that severed the tendon of the middle finger of her right hand.  After a visit to A&E the same day she underwent surgery two days later.  She is now unable to work due to the accident in the workplace.  The employer is a well-known international company and has said that because she had signed a consent form that she knows how to use a knife they will not pay her sick pay for the time off work which will be between 6 - 12 weeks.  The HSE department has not contacted her at any stage to discuss how this happened and how this accident could have been avoided.

My question is should she be liable for sick pay as it was a work-related accident?

The cause of injury being work-related has no legal bearing on whether the employer has to pay sick pay - although you might well think it has a moral bearing on it. 

Sometimes there is a discretionary element to sick pay.  It can be that according to the strict letter of the employer's policy, they are not entitled to company sick pay, but that there is management discretion to pay it anyway.  Of course that can't be relied on, but it might be worth a try.

I agree that the ACAS website is the place to get the authoritative information about sick pay entitlements, particularly statutory sick pay which the employer cannot get out of if the conditions apply.  However statutory sick pay is derisory in value.

There are two things that can never be subject of waiver or disclaimer under UK law - death and injury.

Whilst signing a document stating someone knows how to use a knife may give them a waiver in foreign lands the onus is on UK employers to prove they have provided suitable and sufficient training which even then does not absolve them of certain obligations in the event of injury or death.

This is where work related claims come in - to recover loss of earnings especially where an employer has no or limited sick-pay. Generally good sick pay schemes are put in place to off-set litigation and compensation.

If she is in a union they need to be staring the ball rolling through their solicitors (although based on the knife document comment I suspect there is no one looking after employee rights in this workplace).

I agree with the points made above about making a claim against the employer.  This is why everyone should join a trade union!

My first thought was to PPE or possibly lack thereof.

Does not sound the most caring of employers so I would be ensuring that she is paid her stautory sick pay (which they cannot get out of paying) even though its not that great and seeing a solicitor.

Has she even seen a risk assessment for the task she was carrying out? Sat at my desk I can think of a miriad of hazrads and possible control measures....but that is all in my imaginary workspace.

Good luck, I hope it works out well.  There is more than just sick pay you can claim for, but a solicitor will help you with that.