It all depends really . Are you international or home student ? If you are home , then you need an A* in maths , and also how strong your PS would be . If it was in previous years , i would have told you , you wont a chance with a B in like econ , but with the changes in fees for home/EU students , the Gvt has categorically told universities to give more places to home students since the fees will be much higher compared to previous years where only the very best home students made it to ucl or lse but from what i ve seen this year , its all changed . I ve seen some people with lower grades getting into lse or ucl of which if these very same applicants had applied in the previous cycles , they wouldn't have been allowed through the gates , so its worth a try .
On another note , your subjects are strong so that should put you in good stead , try have an A* in maths and i m sure you will get in . Good luck .