Assistance and Welfare - Important Advice 
It is very important that if your flight is delayed and your holiday company or airline advises you not to check-in you ask your airline/holiday company to confirm that you still have the same rights as someone who has checked-in. Ask for confirmation in writing/text or email. 
The reason for this is because Regulation (EC) 261/2004 only applies to those passengers who have checked-in. 
The importance of ensuring you are protected by the Regulation is that the protection means that the airline is obligated to meet the costs of assisting you – for example providing meals and refreshments and, if applicable, hotel accommodation during a delay. 
Sometimes airlines fail to provide the services they are supposed to provide such as food, refreshments and accommodation. If your airline does not offer or provide assistance and you incur expenses then ensure you keep all the receipts you are given. You will need to produce proof of your 'necessarily' incurred expenses when you try to reclaim them at a later date. Without proof of your out of pocket expenses you may find that the airline will only offer to repay a proportion of your expenses. 
You should carefully check any insurance policies you have to find out if your insurer can provide you with assistance and also what, if any, benefits you are entitled to because your flight is delayed. 
EU Countries 
Regulation (EC) 261/2004 only applies to member states of the European Union, European Economic Area and Switzerland. 
Further Information 
For further information about passenger rights and for free advice please contact the Air Transport User’s Council by visiting http://www.auc.org.uk/ or by calling telephone 020 7240 6061. 
The Air Transport User’s Council is the UK’s consumer council for air travel and is funded by the Civil Aviation Authority. 
Other useful websites are: 
Montreal Convention - http://www.legislation.gov.uk/uksi/2002/263/contents/made Regulation (EC) 261/2004 - http://www.auc.org.uk/default.aspx?catid=306&pagetype=90&pageid=6547