what is the best way ...cheapest to transfer

Deals_2

euros to a uk account. can we use paypal? payment to be made to a nationwide account.

Olipro

ask the sending bank about making a SEPA payment (if the bank is in the EU which I would imagine it probably is.)

Nationwide do not charge for incoming payments and conversion is done at the wholesale rate.

System

According to Nationwide's website, Flexaccounts can receive payments from the EU only if they are sent by the expensive legacy SWIFT system, quoting BIC NAIAGB21 as the destination and MIDLGB22 (which is now HSBC) as intermediary.
http://www.nationwide.co.uk/search/DisplayArticle.aspx?article=1572
Most employees of banks in the EU will not understand this, and will try to send the transfer as a (usually free) SEPA Credit Transfer, quoting, as they have to, only one BIC, MIDLGB22. (Their system should tell them that NAIAGB21 is not compliant as a destination BIC for a SEPA Credit Transfer.) A SEPA Credit Transfer sent to MIDLGB22 and a Nationwide IBAN will fail, because Nationwide has not made an arrangement with HSBC for it to be automatically processed 'straight through' to the destination account, as is required by the SEPA Credit Transfer standards.