Hargreaves Lansdown system crashes on Royal Mail trade

There's been some significant annoyance for Royal Mail investors this morning as Hargreaves Landsdown systems buckle under the weight of trading:
We are sincerely sorry for anyone who hasn’t been able to trade this morning and are doing all we can to meet client demand
— Hargreaves Lansdown (@HLInvest) October 11, 2013
All available staff are working on dealing lines and website, we are trading by phone but delays getting through, our sincere apologies
— Hargreaves Lansdown (@HLInvest) October 11, 2013
Customers have taken to social media platform Twitter to complain:
I have 227 shares in Royal Mail but as of 11:15 Hargreaves Lansdown website does not work, phone engaged, internet helpline unobtainable.
— brian kelly (@kellybri) October 11, 2013
FFS @hlinvest this is terrible, cannot even get a dial tone on phone just busy tone so can't even join the queue and cannot access online!
— Alice (@AprincessH2) October 11, 2013
Royal Mail IPO: All sorts of problems trying to access my @HLInvest account this morning. No success as yet. Very frustrating.
— Gary Coombs (@CoogarUK) October 11, 2013