Silence Therapeutics Expands RNAi Structural Modification IP Portfolio With Issuance of New U.S. Patent

Second Recent Patent Issuance Related to Innovative Zamore 'Design Rules'

LONDON, July 7, 2010 - Silence Therapeutics plc (AIM: SLN) ("Silence" or the "Company")
announces the issuance of United States patent 7,750,144, titled Methods and
Compositions for Enhancing Efficacy and Specificity of RNA Silencing, by the
United States Patent and Trademark Office (USPTO). The issued patent
generally claims methods of producing double stranded (RNAi) agents having
decreased off-target silencing activity through certain structural
modifications. The ability to minimize the off-target effects of RNAi
therapeutics is critical for controlling unwanted cellular activity and/or
potential safety concerns. The issued claims not only cover minimizing
off-target gene expression silencing using short interfering RNA (siRNA) but
also include specific claims directed to micro RNA (miRNA).

This latest issued patent is based on the seminal research of Phillip D.
Zamore, Ph.D., Howard Hughes Medical Institute Investigator, the Gretchen
Stone Cook Chair of Biomedical Sciences, and Professor of Biochemistry &
Molecular Pharmacology at University of Massachusetts Medical School. Silence
owns exclusive licenses in the human healthcare fields to three Zamore patent
families from the University of Massachusetts Medical School, where Zamore is
the co-director of the RNA Therapeutics Institute. These patent families
disclose various efficacy-enhancing methods and structural elements for RNAi
therapeutics, informally known as the Zamore "Design Rules" and based on Dr.
Zamore's work at UMass Medical School. This is the third patent to issue
among the Zamore design rule patents licensed by UMass Medical School to
Silence. The Company expects additional U.S. and European patent issuances
related to the Zamore portfolio in the coming months.

"This latest in a series of related patent issuances continues to
highlight the significant value of the groundbreaking Zamore patent families.
For the second time in the past month, we have strengthened our rapidly
expanding RNAi IP position with a key patent issuance in the area of
structural modification technology," stated Philip Haworth, Ph.D., chief
executive officer of Silence Therapeutics. "Whereas our last patent provided
key guidance in enhancing the desired silencing activity of RNAi agents, this
latest patent covers the equally valuable ability to minimize the undesired
off-target silence activity of RNAi agents."

Silence Therapeutics is executing a proactive strategy to continue to
build and strengthen a diverse and competitive intellectual property
portfolio that provides the company and its partners with a strong
proprietary position in the RNAi therapeutics space. The company believes
that it will continue to make significant progress in these efforts
throughout 2010 as it expects a number of additional valuable RNAi patents to
be issued in both the United States and Europe during the year. This
consistent and meaningful IP portfolio growth reinforces Silence's belief
that the company can sustain its position as a preferred partner in RNAi
therapeutics. At present, Silence's global patent portfolio contains issued
patents and pending applications covering strategic areas of RNAi therapeutic
development including multiple proprietary siRNA delivery technologies,
potent siRNA sequences specific for high-value disease targets and key RNAi
sequence and chemical modifications.

About Silence Therapeutics plc (www.silence-therapeutics.com)

Silence Therapeutics plc (AIM: SLN) is a leading global biotechnology
company dedicated to the discovery, development and delivery of targeted,
systemic RNA interference (RNAi) therapeutics for the treatment of serious
diseases. The company possesses multiple proprietary short interfering RNA
(siRNA) delivery technology platforms including AtuPLEX(TM), a system that
enables the functional delivery of siRNA molecules to targeted diseased
tissues and cells, while increasing their bioavailability and intracellular
uptake. A second, complementary delivery technology known as PolyTran(TM)
uses a library of novel peptide-based biodegradable polycationic polymers for
systemic siRNA administration. Additionally, the company has a platform of
novel siRNA molecules, AtuRNAi, which provide a number of advantages over
conventional siRNA molecules, including increased stability against nuclease
degradation. Silence's unique RNAi assets also include structural features
for a next generation of RNAi molecules and additional proprietary siRNA
sequences against more than 50 highly valued oncology and other disease
targets.

The company's strong and diverse intellectual property portfolio includes
exclusive licenses from the University of Massachusetts Medical School on
three patent families associated with the Zamore "Design Rules," which cover
broad structural features of siRNA design for more potent next generation
siRNA sequences.

Silence Therapeutics is headquartered in London, UK, with research and
development activities in Berlin and operations in Redwood City, CA.

About UMass Medical School

The University of Massachusetts Medical School, one of the fastest
growing academic health centers in the country, has built a reputation as a
world-class research institution, consistently producing noteworthy advances
in clinical and basic research. The Medical School attracts more than US$240
million in research funding annually, 80 percent of which comes from federal
funding sources. UMMS is the academic partner of UMass Memorial Health Care,
the largest health care provider in Central Massachusetts. For more
information visit www.umassmed.edu.

Forward-Looking Statements

This press release includes forward-looking statements that are subject
to risks, uncertainties and other factors. These risks and uncertainties
could cause actual results to differ materially from those referred to in the
forward-looking statements. All forward-looking statements are based on
information currently available to Silence Therapeutics and Silence
Therapeutics assumes no obligation to update any such forward-looking
statements.

Phil Haworth of Silence Therapeutics, +1-650-855-1514, p.haworth at silence-therapeutics.com, or Tim Brons (media) or Stephanie Diaz (investors), +1-415-675-7400, tbrons at vidacommunication.com or sdiaz at vidacommunication.com, both of Vida Communication for Silence Therapeutics, or Richard Potts / Jonathan Senior of Nomura Code Securities, +44-20-7776-1200, or Mary-Jane Elliott / Emma Thompson of M:Communications, +44-20-7920-2342