After posting here I sent and e-mail to Yahoo to see if they could shed any light on the matter, about an hour later my mail started working again, although I have no idea what the problem was or how it was fixed!?
If it helps anyone they have given me a pretty comprehensive response of different things to try, see below:
Thanks for writing to Yahoo! UK Customer Care.
POP3 and SMTP access is a free service for users with yahoo.co.uk
addresses. If you would like to be able to send and receive Yahoo! Mail
through an email client, please follow the steps below:
1. Click the "Options" link, and choose "Mail Options/More Options..."
2. Click the "POP Access and Forwarding" link on the Options screen.
3. In the new window, click the radio button beside "Allow your Yahoo!
Mail to be POPed," and then click "Save Changes"
To configure the MAC Mail client (10.0 or 10.1) for POP Access, please
follow the directions below:
1. To begin, open up the email client.
2. Click "Mail" from the top menu, and select "Preferences" from the
pull-down menu.
3. On the "Mail Preferences" screen, select the "Create Account" button.
4. On the "Account Type" pull down menu, select "POP Account."
5. In the "Description" field, enter a descriptive title-for example
"Yahoo! Email."
6. Enter your Yahoo! email address and full name in the space provided.
7. Next to "Host name" type: pop.mail.yahoo.co.uk.
8. Under "User Name," enter your Yahoo! ID without the "@yahoo.co.uk."
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There are a number of factors that could cause difficulties with POP and
SMTP access, and you'll find most of them outlined below. We realise
this message is long and technical in nature, but we're hopeful that
with your help, we can resolve the issue.
I. Check settings
* Incoming Mail (POP3) Server: pop.mail.yahoo.co.uk (port 995 SSL)
* Outgoing (SMTP) Server: smtp.mail.yahoo.co.uk (port 465 SSL)
* Account Name/Login Name: Your Yahoo! Mail name in lowercase (your
address without the "@yahoo.co.uk").
To find the POP/SMTP settings specific to your email client, please
visit the following page:
http://help.yahoo.com/l/uk/yahoo/mail/yahoomail/pop/
II. Check that your password hasn't changed
1. Log in to Yahoo! Mail on the web
http://uk.mail.yahoo.com/
IMPORTANT: If you have problems logging into your web-based account,
please respond and let us know the exact error message that appears.
III. Problems sending messages
Please ensure that you have configured your email client to authenticate
during the SMTP session. For more information, please visit:
http://help.yahoo.com/l/uk/yahoo/mail/yahoomail/pop/pop-32.html
If you've double-checked the items above but continue to have problems
sending messages, it is very likely that your ISP may block connections
to external outgoing mail servers. To clarify this, please ask your ISP,
whether they allow users to send mail from SMTP servers that are not on
their network. If not, you will need to enter your ISP's outgoing mail
server in place of Yahoo!'s outgoing mail server in your email client.
IV. Problems retrieving messages.
Corrupt messages within your Yahoo! Mail account can prevent successful
pop sessions to occur within your email client. If there is a damaged
message in your mailbox, we suggest that you log into your Yahoo! Mail
account via the web and move the contents of your Inbox to a different
folder.
You can do this by following the instructions below:
Yahoo! Mail Classic:
1. Add a new personal folder by clicking the "Add" link next to "My
folders."
2. In the window which pops up enter a new folder name.
3. Click "OK."
4. Return to your Inbox, by clicking on the "Inbox" link within your
folder list.
5. Scroll to the bottom of the page, and check the "Check all" box.
6. Click the "Move" button.
7. Select the destination folder from the pull-down menu.
8. The messages will be transferred at once.
All New Mail:
1. Add a new personal folder by clicking the "Add" link next to "My
Folders."
2. Enter a new name for your folder.
3. Press "Enter" on your keyboard.
4. Return to your Inbox, by clicking on the "Inbox" link within your
folder list.
5. Tick the box to select all messages (it is located near the "From"
header on the inbox toolbar above the message list).
6. Click the "Move" button.
7. Select the destination folder from the pull-down menu.
8. The messages will be transferred at once.
Once this is done, please sign out of your account, and return to your
email client and proceed to POP your mail.
After this step, return to your Mail account and proceed with moving the
messages back to your Inbox in small increments, until you find your
corrupt message and can delete it.
If you've double-checked the items above but continue to have problems
receiving messages, your difficulty is most likely caused by issues
specific to your local network. If you connect to the Internet using a
LAN with a proxy server or a firewall, you may need special settings to
access external mail servers. For further information, please contact
your LAN administrator.
We realise this message was long and contained many technical
troubleshooting recommendations, and we appreciate you taking the time
to follow through the steps provided.
If the troubleshooting steps listed above do not resolve your issue, you
can either reply to this email including the results of any tests with
the response or you can also chat with us LIVE using Yahoo! Mail Live
Chat Support! Just copy the following link and paste it into the address
bar of a browser:
http://help.yahoo.com/l/uk/yahoo/mail/contactchat/formsindex.html
Then just click on the "Chat with us live now" button, and you'll be
connected to one of our Yahoo! Chat agents.
