Share price data appears to currently inaccurate in My Portfolio. I have cross checked with Uday and my UK broker (Interactive Investor) They have identical share prices and significantly different from Yahoo Finance. I have done these cross-checks in the past and there has never been a problem. The price of AstraZeneca (one of the biggest) is about 5GBP different (about 3%).
You seem to have a problem in your system.
Regards
Dr John Dalziel