For proper legal advice you should consult a solicitor, but...
Under section 11 of the Package Travel, Package Holidays and Package Tours Regulations 1992 the only price increases allowed are those for increased transport costs (fuel prices, etc), increased taxes and exchange rate fluctuations.
Section 12 requires the operator to notify the consumer of any significant changes (to what was in the brochure) as soon as possible, and grants the consumer the right to cancel WITHOUT PENALTY, or to accept the changes.
If you are unwilling to accept the changes to the holiday you could write to the Tour Operator (as soon as possible), requiring a full refund, and stating that you will take legal action if the refund is not made.
If you're willing to travel 2 days later, and up for a fight, you could write to the Tour Operator and demand either the 2 bedroom apartment or a reduction in price (for the 1 bed). If you cannot agree a new deal you can then cancel anyway.
You should also check the reason for the cost increase, unless it is for one of the reasons above it could be illegal.
Hope this helps.
LS