Whether or not you'll be allowed to enter the UK is a topic for a different forum (and really more a topic for a lawyer rather than strangers on the internet). That being said, as a non-lawyer giving my opinion of the situation, you should be granted access to the UK as the banks/money lenders/phone companies don't have a relationship with Border Entry.
With regards to debts in the UK, there is some precedent to debts being waived after a certain period of time, but the minimum is 6 years for unsecured debt, and the companies you owe money to can still chase you for payment, but can't use legal proceedings to force you to pay. However, the big caveat to this is that this only applies to residents of England and Wales.
From the cleardebt.co.uk site:
What is out of date debt?
Debts like these are covered by the Limitation Act 1980, which is a
statute of limitations that provides time scales as to how long a
creditor can chase you (the debtor) for an unpaid debt. The Limitation
Act 1980 only applies when no acknowledgement of a debt has been made
between you and the creditor for six years for unsecured debts or 12
years for mortgage shortfalls and secured loans. This law only applies
to residents of England and Wales.
When does debt go out of date?
If the creditor fails to maintain contact with you for six years or
more, you may be able to claim that the outstanding debt is statute
barred under the Limitation Act 1980. This means the creditor cannot
use the legal system to enforce payment of the outstanding debt. The
time limit starts from when you last acknowledged owing the debt or
made a payment to the account.
When can a creditor pursue an unsecured debt?
You may think a creditor has written off your debt if you haven’t heard from them for
a long time. The reality is that the debt still exists. The creditor
can still contact you and they are entitled to chase the outstanding
debt, even if the debt has been statute barred, but they are unable to
use legal proceedings to force you to pay. Creditors can pursue an
unsecured debt if:
- The creditor has taken court action against you within the past six years for unsecured debts or 12 years for mortgage shortfalls (e.g.
- You made a payment to the account within the last six (unsecured debts) or 12 years (mortgage shortfalls), which includes people named
on the credit agreement and not just you
- Acknowledgement of the debt has been made in writing and signed by the person making it