I paid 179 pounds which included VAT and breakfast. I booked the rate at Hilton.com.
With the hotel, I have seen rates as low as 99 pounds excluding VAT (which is 17.5%). You might want to check Orbitz, Expedia and Travelocity for exclusive rates. Use Priceline if hotel benefits are not important to you.
http://www.hilton.co.uk/Trafalgar is the hotel's website.